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/SymbolTable.cpp

@@ -178,7 +178,7 @@ void TType::buildMangledName(TString& mangledName) const
     }
 }
 
-#ifndef GLSLANG_WEB
+#if !defined(GLSLANG_WEB) && !defined(GLSLANG_ANGLE)
 
 //
 // Dump functions.