Fix parser issue: redeclare gl_FragStencilRefARB is not supported

Test/spv.shaderStencilExport.frag

@@ -2,6 +2,8 @@
 
 #extension GL_ARB_shader_stencil_export: enable
 
+out int gl_FragStencilRefARB;
+
 void main()
 {
     gl_FragStencilRefARB = 100;

glslang/MachineIndependent/ParseHelper.cpp

@@ -3872,6 +3872,8 @@ TSymbol* TParseContext::redeclareBuiltinVariable(const TSourceLoc& loc, const TS
          identifier == "gl_BackSecondaryColor"                                                      ||
          identifier == "gl_SecondaryColor"                                                          ||
         (identifier == "gl_Color"               && language == EShLangFragment)                     ||
+        (identifier == "gl_FragStencilRefARB"   && (nonEsRedecls && version >= 140)
+                                                && language == EShLangFragment)                     ||
 #ifdef NV_EXTENSIONS
          identifier == "gl_SampleMask"                                                              ||
          identifier == "gl_Layer"                                                                   ||
@@ -3954,6 +3956,12 @@ TSymbol* TParseContext::redeclareBuiltinVariable(const TSourceLoc& loc, const TS
                     error(loc, "all redeclarations must use the same depth layout on", "redeclaration", symbol->getName().c_str());
             }
         }
+        else if (identifier == "gl_FragStencilRefARB") {
+            if (qualifier.hasLayout())
+                error(loc, "cannot apply layout qualifier to", "redeclaration", symbol->getName().c_str());
+            if (qualifier.storage != EvqVaryingOut)
+                error(loc, "cannot change output storage qualification of", "redeclaration", symbol->getName().c_str());
+        }
 #ifdef NV_EXTENSIONS
         else if (identifier == "gl_SampleMask") {
             if (!publicType.layoutOverrideCoverage) {