Keeping track of discard

Shader compilation now keeps track of the discard key word.

Previously only variables were monitored. But discard, which needs
special treatment in some cases, went unnoticed by the compiler as
discard is not a variable but a flow control.

This commit adds monitoring for discard.

drivers/gles2/shader_compiler_gles2.cpp

@@ -704,6 +704,10 @@ String ShaderCompilerGLES2::_dump_node_code(SL::Node *p_node, int p_level, Gener
 				}
 				code += ";\n";
 			} else if (cf_node->flow_op == SL::FLOW_OP_DISCARD) {
+				if (p_actions.usage_flag_pointers.has("DISCARD") && !used_flag_pointers.has("DISCARD")) {
+					*p_actions.usage_flag_pointers["DISCARD"] = true;
+					used_flag_pointers.insert("DISCARD");
+				}
 				code += "discard;";
 			} else if (cf_node->flow_op == SL::FLOW_OP_CONTINUE) {
 				code += "continue;";

drivers/gles3/shader_compiler_gles3.cpp

@@ -700,6 +700,11 @@ String ShaderCompilerGLES3::_dump_node_code(SL::Node *p_node, int p_level, Gener
 				}
 			} else if (cfnode->flow_op == SL::FLOW_OP_DISCARD) {
 
+				if (p_actions.usage_flag_pointers.has("DISCARD") && !used_flag_pointers.has("DISCARD")) {
+					*p_actions.usage_flag_pointers["DISCARD"] = true;
+					used_flag_pointers.insert("DISCARD");
+				}
+
 				code = "discard;";
 			} else if (cfnode->flow_op == SL::FLOW_OP_CONTINUE) {