GLSL: Disallow 'shared' in nested scopes.

This implements Khronos-private specification bug 16130.

Test/450.comp

 #version 450 core
-layout(local_size_x = 0) in; // ERROR, 0 not allowed
\ No newline at end of file
+layout(local_size_x = 0) in; // ERROR, 0 not allowed
+void main()
+{
+    shared float f;   // ERROR shared must be global
+}

Test/baseResults/450.comp.out

 450.comp
 ERROR: 0:2: 'local_size_x' : must be at least 1 
-ERROR: 1 compilation errors.  No code generated.
+ERROR: 0:5: 'shared' : not allowed in nested scope 
+ERROR: 2 compilation errors.  No code generated.
 
 
 Shader version: 450
 local_size = (1, 1, 1)
 ERROR: node is still EOpNull!
+0:3  Function Definition: main( ( global void)
+0:3    Function Parameters: 
 0:?   Linker Objects
 
 
 Linked compute stage:
 
-ERROR: Linking compute stage: Missing entry point: Each stage requires one entry point
 
 Shader version: 450
 local_size = (1, 1, 1)
 ERROR: node is still EOpNull!
+0:3  Function Definition: main( ( global void)
+0:3    Function Parameters: 
 0:?   Linker Objects
 

glslang/MachineIndependent/glslang.y

@@ -1231,6 +1231,7 @@ storage_qualifier
         $$.qualifier.storage = EvqBuffer;
     }
     | SHARED {
+        parseContext.globalCheck($1.loc, "shared");
         parseContext.profileRequires($1.loc, ECoreProfile | ECompatibilityProfile, 430, E_GL_ARB_compute_shader, "shared");
         parseContext.profileRequires($1.loc, EEsProfile, 310, 0, "shared");
         parseContext.requireStage($1.loc, EShLangCompute, "shared");