Use GLSLANG_ANGLE to strip features to what ANGLE requires

This change strips a few features similar to GLSLANG_WEB but doesn't
remove every detail like the latter.  It also hardcodes profile/version
to core/450.

In particular, TBuiltIns::initialize is specialized to remove most of
what is not supported or won't be supported by ANGLE.  The result of
this function is parsed with TParseContext::parseShaderStrings which is
a performance bottleneck.

This change shaves about 300KB off of ANGLE's binary size and reduces
the cost of SetupBuiltinSymbolTable to nearly a sixth.

Signed-off-by: Shahbaz Youssefi <ShabbyX@gmail.com>

glslang/MachineIndependent/iomapper.h

@@ -33,7 +33,7 @@
 // POSSIBILITY OF SUCH DAMAGE.
 //
 
-#ifndef GLSLANG_WEB
+#if !defined(GLSLANG_WEB) && !defined(GLSLANG_ANGLE)
 
 #ifndef _IOMAPPER_INCLUDED
 #define _IOMAPPER_INCLUDED
@@ -186,7 +186,7 @@ protected:
     }
 };
 
-// Defaulf I/O resolver for OpenGL
+// Default I/O resolver for OpenGL
 struct TDefaultGlslIoResolver : public TDefaultIoResolverBase {
 public:
     typedef std::map<TString, int> TVarSlotMap;  // <resourceName, location/binding>
@@ -299,4 +299,4 @@ public:
 
 #endif // _IOMAPPER_INCLUDED
 
-#endif //  GLSLANG_WEB
+#endif // !GLSLANG_WEB && !GLSLANG_ANGLE