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/parseVersions.h

@@ -58,7 +58,7 @@ public:
                    const SpvVersion& spvVersion, EShLanguage language, TInfoSink& infoSink,
                    bool forwardCompatible, EShMessages messages)
         :
-#ifndef GLSLANG_WEB
+#if !defined(GLSLANG_WEB) && !defined(GLSLANG_ANGLE)
         forwardCompatible(forwardCompatible),
         profile(profile),
 #endif
@@ -116,9 +116,14 @@ public:
     bool relaxedErrors()    const { return false; }
     bool suppressWarnings() const { return true; }
     bool isForwardCompatible() const { return false; }
+#else
+#ifdef GLSLANG_ANGLE
+    const bool forwardCompatible = true;
+    const EProfile profile = ECoreProfile;
 #else
     bool forwardCompatible;      // true if errors are to be given for use of deprecated features
     EProfile profile;            // the declared profile in the shader (core by default)
+#endif
     bool isEsProfile() const { return profile == EEsProfile; }
     void requireProfile(const TSourceLoc& loc, int profileMask, const char* featureDesc);
     void profileRequires(const TSourceLoc& loc, int profileMask, int minVersion, int numExtensions,