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>

SPIRV/GlslangToSpv.cpp

@@ -281,6 +281,8 @@ spv::SourceLanguage TranslateSourceLanguage(glslang::EShSource source, EProfile
 {
 #ifdef GLSLANG_WEB
     return spv::SourceLanguageESSL;
+#elif defined(GLSLANG_ANGLE)
+    return spv::SourceLanguageGLSL;
 #endif
 
     switch (source) {
@@ -8684,7 +8686,7 @@ void OutputSpvBin(const std::vector<unsigned int>& spirv, const char* baseName)
 // Write SPIR-V out to a text file with 32-bit hexadecimal words
 void OutputSpvHex(const std::vector<unsigned int>& spirv, const char* baseName, const char* varName)
 {
-#ifndef GLSLANG_WEB
+#if !defined(GLSLANG_WEB) && !defined(GLSLANG_ANGLE)
     std::ofstream out;
     out.open(baseName, std::ios::binary | std::ios::out);
     if (out.fail())