GL_EXT_control_flow_attributes2 support. (#3531)

The actual support has been available with GL_EXT_control_flow_attributes.
This change set is to handle
  "#extension GL_EXT_control_flow_attributes2 : <val>"

Test/baseResults/460.frag.out

@@ -1,5 +1,7 @@
 460.frag
-ERROR: 0:22: 'attribute' : required extension not requested: GL_EXT_control_flow_attributes
+ERROR: 0:22: 'attribute' : required extension not requested: Possible extensions include:
+GL_EXT_control_flow_attributes
+GL_EXT_control_flow_attributes2
 ERROR: 0:23: 'attribute' : required extension not requested: GL_EXT_control_flow_attributes
 ERROR: 0:30: 'dependency_length' : must be positive 
 ERROR: 0:31: 'dependency_length' : must be positive 

glslang/MachineIndependent/Versions.cpp

@@ -264,6 +264,8 @@ void TParseVersions::initializeExtensionBehavior()
     extensionBehavior[E_GL_EXT_fragment_shader_barycentric]             = EBhDisable;
     extensionBehavior[E_GL_EXT_expect_assume]                           = EBhDisable;
 
+    extensionBehavior[E_GL_EXT_control_flow_attributes2]                = EBhDisable;
+
     extensionBehavior[E_GL_KHR_cooperative_matrix]                      = EBhDisable;
 
     // #line and #include
@@ -591,6 +593,8 @@ void TParseVersions::getPreamble(std::string& preamble)
             "#define GL_EXT_fragment_shader_barycentric 1\n"
             "#define GL_EXT_shader_quad_control 1\n"
             "#define GL_EXT_texture_array 1\n"
+
+            "#define GL_EXT_control_flow_attributes2 1\n"
             ;
 
         if (spvVersion.spv == 0) {

glslang/MachineIndependent/Versions.h

@@ -221,6 +221,7 @@ const char* const E_GL_EXT_draw_instanced                   = "GL_EXT_draw_insta
 const char* const E_GL_EXT_texture_array                    = "GL_EXT_texture_array";
 const char* const E_GL_EXT_maximal_reconvergence            = "GL_EXT_maximal_reconvergence";
 const char* const E_GL_EXT_expect_assume                    = "GL_EXT_expect_assume";
+const char* const E_GL_EXT_control_flow_attributes2         = "GL_EXT_control_flow_attributes2";
 
 // Arrays of extensions for the above viewportEXTs duplications
 

glslang/MachineIndependent/glslang.y

@@ -3950,7 +3950,8 @@ iteration_statement
         $$ = $1;
     }
     | attribute iteration_statement_nonattributed {
-        parseContext.requireExtensions($2->getLoc(), 1, &E_GL_EXT_control_flow_attributes, "attribute");
+        const char * extensions[2] = { E_GL_EXT_control_flow_attributes, E_GL_EXT_control_flow_attributes2 };
+        parseContext.requireExtensions($2->getLoc(), 2, extensions, "attribute");
         parseContext.handleLoopAttributes(*$1, $2);
         $$ = $2;
     }