Fix an issue of getExtBuiltins()

This function is used to import SPIR-V extended instruction set. It
mistakenly treated the name of SPIR-V extended instruction set as the
name of SPIR-V extension. For example, when we have such code

  getExtBuiltins("NonSemantic.DebugBreak")

'NonSemantic.DebugBreak' is added to SPIR-V extension. Rather, the
SPIR-V extension name should be 'SPV_KHR_non_semantics_info'. Therefore,
we must avoid this since the name of SPIR-V extended instruction set is
not necessarily equal to that of relevant SPIR-V extension. Adding a
SPIR-V extension must be done by calling addExtension() explicitly
outside this function.

This change also fixes disassembly issues of debugBreak().

SPIRV/GlslangToSpv.cpp

@@ -10222,7 +10222,6 @@ spv::Id TGlslangToSpvTraverser::getExtBuiltins(const char* name)
     if (extBuiltinMap.find(name) != extBuiltinMap.end())
         return extBuiltinMap[name];
     else {
-        builder.addExtension(name);
         spv::Id extBuiltins = builder.import(name);
         extBuiltinMap[name] = extBuiltins;
         return extBuiltins;