Fix building issues on some mac systems (#570)

Makefile

@@ -82,7 +82,7 @@ else ifeq ($(UNAME),Darwin)
 # Mac
 LIBEXT=dylib
 CFLAGS += -m$(MARCH) -I include -I /usr/local/include -I /usr/local/opt/libjpeg-turbo/include \
-	-I /usr/local/opt/jpeg-turbo/include -I /usr/local/opt/sdl2/include/SDL2 -I /usr/local/opt/libvorbis/include \
+	-I /usr/local/opt/jpeg-turbo/include -I /usr/local/opt/sdl2/include -I /usr/local/opt/libvorbis/include \
 	-I /usr/local/opt/openal-soft/include -Dopenal_soft  -DGL_SILENCE_DEPRECATION
 LFLAGS += -Wl,-export_dynamic -L/usr/local/lib
 

libs/sdl/gl.c

@@ -7,7 +7,7 @@
 #	include <OpenGLES/ES3/gl.h>
 #	define HL_GLES
 #elif defined(HL_MAC)
-#	include <SDL.h>
+#	include <SDL2/SDL.h>
 #	include <OpenGL/gl3.h>
 #	define glBindImageTexture(...) hl_error("Not supported on OSX")
 #	define glDispatchCompute(...) hl_error("Not supported on OSX")

libs/sdl/sdl.c

@@ -6,8 +6,6 @@
 #if defined(_WIN32) || defined(__ANDROID__) || defined(HL_IOS) || defined(HL_TVOS)
 #	include <SDL.h>
 #	include <SDL_syswm.h>
-#elif defined(HL_MAC)
-#	include <SDL.h>
 #else
 #	include <SDL2/SDL.h>
 #endif

other/cmake/FindSDL2.cmake

@@ -76,12 +76,21 @@ SET(SDL2_SEARCH_PATHS
 	${SDL2_PATH}
 )
 
-FIND_PATH(SDL2_INCLUDE_DIR SDL.h
-	HINTS
-	$ENV{SDL2DIR}
-	PATH_SUFFIXES include/SDL2 include
-	PATHS ${SDL2_SEARCH_PATHS}
-)
+if (APPLE)
+	FIND_PATH(SDL2_INCLUDE_DIR SDL2/SDL.h
+		HINTS
+		$ENV{SDL2DIR}
+		PATH_SUFFIXES include/SDL2 include
+		PATHS ${SDL2_SEARCH_PATHS}
+	)
+else()
+	FIND_PATH(SDL2_INCLUDE_DIR SDL.h
+		HINTS
+		$ENV{SDL2DIR}
+		PATH_SUFFIXES include/SDL2 include
+		PATHS ${SDL2_SEARCH_PATHS}
+	)
+endif()
 
 if(CMAKE_SIZEOF_VOID_P EQUAL 8)
 	set(PATH_SUFFIXES lib64 lib/x64 lib)