Fix various Clang 7 warnings about unused stuff

Namely:
[-Wunneeded-internal-declaration]
[-Wunused-comparison]
[-Wunused-const-variable]
[-Wunused-function]
[-Wunused-private-fields]

Fixes the following Clang 7 warnings:
```
editor/plugins/script_editor_plugin.cpp:1417:20: warning: function '_find_node_with_script' is not needed and will not be emitted [-Wunneeded-internal-declaration]
editor/scene_tree_dock.cpp:1859:14: warning: function '_find_last_visible' is not needed and will not be emitted [-Wunneeded-internal-declaration]

modules/gdscript/gdscript_parser.cpp:7838:19: warning: equality comparison result unused [-Wunused-comparison]

scene/resources/mesh.cpp:549:35: warning: unused variable '_array_types' [-Wunused-const-variable]
scene/resources/mesh.cpp:563:18: warning: unused variable '_format_translate' [-Wunused-const-variable]

drivers/gles3/rasterizer_scene_gles3.cpp:54:28: warning: unused function 'store_transform2d' [-Wunused-function]

core/io/file_access_network.h:50:6: warning: private field 'ml' is not used [-Wunused-private-field]
core/io/file_access_zip.h:93:14: warning: private field 'archive' is not used [-Wunused-private-field]
core/io/resource_format_binary.h:122:6: warning: private field 'bin_meta_idx' is not used [-Wunused-private-field]
core/message_queue.h:47:9: warning: private field 'mutex' is not used [-Wunused-private-field]
main/tests/test_gui.cpp:63:11: warning: private field 'control' is not used [-Wunused-private-field]
modules/gdscript/gdscript_parser.h:558:7: warning: private field 'completion_static' is not used [-Wunused-private-field]
platform/x11/os_x11.h:148:11: warning: private field 'ip_unix' is not used [-Wunused-private-field]
platform/x11/os_x11.h:180:7: warning: private field 'net_wm_icon' is not used [-Wunused-private-field]
platform/x11/os_x11.h:189:6: warning: private field 'audio_driver_index' is not used [-Wunused-private-field]
platform/x11/os_x11.h:190:15: warning: private field 'capture_idle' is not used [-Wunused-private-field]
servers/physics/body_pair_sw.h:79:6: warning: private field 'cc' is not used [-Wunused-private-field]
servers/visual/visual_server_raster.h:62:7: warning: private field 'draw_extra_frame' is not used [-Wunused-private-field]
```

core/io/file_access_network.h

@@ -47,8 +47,6 @@ class FileAccessNetworkClient {
 		int size;
 	};
 
-	int ml;
-
 	List<BlockRequest> block_requests;
 
 	Semaphore *sem;

core/io/file_access_zip.h

@@ -90,8 +90,6 @@ class FileAccessZip : public FileAccess {
 
 	mutable bool at_eof;
 
-	ZipArchive *archive;
-
 public:
 	virtual Error _open(const String &p_path, int p_mode_flags); ///< open a file
 	virtual void close(); ///< close a file

core/io/resource_format_binary.h

@@ -119,7 +119,6 @@ class ResourceFormatSaverBinaryInstance {
 	bool skip_editor;
 	bool big_endian;
 	bool takeover_paths;
-	int bin_meta_idx;
 	FileAccess *f;
 	String magic;
 	Set<RES> resource_set;

core/message_queue.h

@@ -32,7 +32,6 @@
 #define MESSAGE_QUEUE_H
 
 #include "core/object.h"
-#include "core/os/mutex.h"
 #include "core/os/thread_safe.h"
 
 class MessageQueue {
@@ -44,8 +43,6 @@ class MessageQueue {
 		DEFAULT_QUEUE_SIZE_KB = 1024
 	};
 
-	Mutex *mutex;
-
 	enum {
 		TYPE_CALL,
 		TYPE_NOTIFICATION,

drivers/gles3/rasterizer_scene_gles3.cpp

@@ -51,26 +51,6 @@ static const GLenum _cube_side_enum[6] = {
 
 };
 
-static _FORCE_INLINE_ void store_transform2d(const Transform2D &p_mtx, float *p_array) {
-
-	p_array[0] = p_mtx.elements[0][0];
-	p_array[1] = p_mtx.elements[0][1];
-	p_array[2] = 0;
-	p_array[3] = 0;
-	p_array[4] = p_mtx.elements[1][0];
-	p_array[5] = p_mtx.elements[1][1];
-	p_array[6] = 0;
-	p_array[7] = 0;
-	p_array[8] = 0;
-	p_array[9] = 0;
-	p_array[10] = 1;
-	p_array[11] = 0;
-	p_array[12] = p_mtx.elements[2][0];
-	p_array[13] = p_mtx.elements[2][1];
-	p_array[14] = 0;
-	p_array[15] = 1;
-}
-
 static _FORCE_INLINE_ void store_transform(const Transform &p_mtx, float *p_array) {
 	p_array[0] = p_mtx.basis.elements[0][0];
 	p_array[1] = p_mtx.basis.elements[1][0];

editor/plugins/script_editor_plugin.cpp

@@ -1414,21 +1414,6 @@ void ScriptEditor::notify_script_changed(const Ref<Script> &p_script) {
 	emit_signal("editor_script_changed", p_script);
 }
 
-static const Node *_find_node_with_script(const Node *p_node, const RefPtr &p_script) {
-
-	if (p_node->get_script() == p_script)
-		return p_node;
-
-	for (int i = 0; i < p_node->get_child_count(); i++) {
-
-		const Node *result = _find_node_with_script(p_node->get_child(i), p_script);
-		if (result)
-			return result;
-	}
-
-	return NULL;
-}
-
 void ScriptEditor::get_breakpoints(List<String> *p_breakpoints) {
 
 	for (int i = 0; i < tab_container->get_child_count(); i++) {

editor/scene_tree_dock.cpp

@@ -1856,32 +1856,6 @@ static bool _has_visible_children(Node *p_node) {
 	return false;
 }
 
-static Node *_find_last_visible(Node *p_node) {
-
-	Node *last = NULL;
-
-	bool collapsed = p_node->is_displayed_folded();
-
-	if (!collapsed) {
-		for (int i = 0; i < p_node->get_child_count(); i++) {
-			if (_is_node_visible(p_node->get_child(i))) {
-				last = p_node->get_child(i);
-			}
-		}
-	}
-
-	if (last) {
-		Node *lastc = _find_last_visible(last);
-		if (lastc)
-			last = lastc;
-
-	} else {
-		last = p_node;
-	}
-
-	return last;
-}
-
 void SceneTreeDock::_normalize_drop(Node *&to_node, int &to_pos, int p_type) {
 
 	to_pos = -1;

main/tests/test_gui.cpp

@@ -60,8 +60,6 @@ namespace TestGUI {
 
 class TestMainLoop : public SceneTree {
 
-	Control *control;
-
 public:
 	virtual void request_quit() {
 

modules/gdscript/gdscript_parser.cpp

@@ -7835,7 +7835,7 @@ void GDScriptParser::_check_block_types(BlockNode *p_block) {
 							// Figure out function name for warning
 							String func_name = _find_function_name(op);
 							if (func_name.empty()) {
-								func_name == "<undetected name>";
+								func_name = "<undetected name>";
 							}
 							_add_warning(GDScriptWarning::RETURN_VALUE_DISCARDED, op->line, func_name);
 						}

modules/gdscript/gdscript_parser.h

@@ -555,7 +555,6 @@ private:
 
 	CompletionType completion_type;
 	StringName completion_cursor;
-	bool completion_static;
 	Variant::Type completion_built_in_constant;
 	Node *completion_node;
 	ClassNode *completion_class;

platform/x11/os_x11.h

@@ -34,17 +34,17 @@
 #include "context_gl_x11.h"
 #include "core/os/input.h"
 #include "crash_handler_x11.h"
-#include "drivers/unix/os_unix.h"
-#include "servers/visual_server.h"
-//#include "servers/visual/visual_server_wrap_mt.h"
 #include "drivers/alsa/audio_driver_alsa.h"
 #include "drivers/alsamidi/alsa_midi.h"
 #include "drivers/pulseaudio/audio_driver_pulseaudio.h"
+#include "drivers/unix/os_unix.h"
 #include "joypad_linux.h"
 #include "main/input_default.h"
 #include "power_x11.h"
 #include "servers/audio_server.h"
 #include "servers/visual/rasterizer.h"
+#include "servers/visual_server.h"
+//#include "servers/visual/visual_server_wrap_mt.h"
 
 #include <X11/Xcursor/Xcursor.h>
 #include <X11/Xlib.h>
@@ -145,7 +145,6 @@ class OS_X11 : public OS_Unix {
 	void handle_key_event(XKeyEvent *p_event, bool p_echo = false);
 	void process_xevents();
 	virtual void delete_main_loop();
-	IP_Unix *ip_unix;
 
 	bool force_quit;
 	bool minimized;
@@ -177,8 +176,6 @@ class OS_X11 : public OS_Unix {
 	AudioDriverPulseAudio driver_pulseaudio;
 #endif
 
-	Atom net_wm_icon;
-
 	PowerX11 *power_manager;
 
 	bool layered_window;
@@ -186,8 +183,6 @@ class OS_X11 : public OS_Unix {
 	CrashHandler crash_handler;
 
 	int video_driver_index;
-	int audio_driver_index;
-	unsigned int capture_idle;
 	bool maximized;
 	//void set_wm_border(bool p_enabled);
 	void set_wm_fullscreen(bool p_enabled);

scene/resources/mesh.cpp

@@ -546,33 +546,6 @@ void Mesh::clear_cache() const {
 Mesh::Mesh() {
 }
 
-static const ArrayMesh::ArrayType _array_types[] = {
-
-	ArrayMesh::ARRAY_VERTEX,
-	ArrayMesh::ARRAY_NORMAL,
-	ArrayMesh::ARRAY_TANGENT,
-	ArrayMesh::ARRAY_COLOR,
-	ArrayMesh::ARRAY_TEX_UV,
-	ArrayMesh::ARRAY_TEX_UV2,
-	ArrayMesh::ARRAY_BONES,
-	ArrayMesh::ARRAY_WEIGHTS,
-	ArrayMesh::ARRAY_INDEX
-};
-
-/* compatibility */
-static const int _format_translate[] = {
-
-	ArrayMesh::ARRAY_FORMAT_VERTEX,
-	ArrayMesh::ARRAY_FORMAT_NORMAL,
-	ArrayMesh::ARRAY_FORMAT_TANGENT,
-	ArrayMesh::ARRAY_FORMAT_COLOR,
-	ArrayMesh::ARRAY_FORMAT_TEX_UV,
-	ArrayMesh::ARRAY_FORMAT_TEX_UV2,
-	ArrayMesh::ARRAY_FORMAT_BONES,
-	ArrayMesh::ARRAY_FORMAT_WEIGHTS,
-	ArrayMesh::ARRAY_FORMAT_INDEX,
-};
-
 bool ArrayMesh::_set(const StringName &p_name, const Variant &p_value) {
 
 	String sname = p_name;

servers/physics/body_pair_sw.h

@@ -76,7 +76,6 @@ class BodyPairSW : public ConstraintSW {
 	Contact contacts[MAX_CONTACTS];
 	int contact_count;
 	bool collided;
-	int cc;
 
 	static void _contact_added_callback(const Vector3 &p_point_A, const Vector3 &p_point_B, void *p_userdata);
 

servers/visual/visual_server_raster.h

@@ -59,7 +59,6 @@ class VisualServerRaster : public VisualServer {
 	};
 
 	static int changes;
-	bool draw_extra_frame;
 	RID test_cube;
 
 	int black_margin[4];