Use temporary parser for mangled names

Use a temporary parser to retrieve the mangled names of specific
function overloads. This is necessary for GL_EXT_texture_shadow_lod.

glslang/MachineIndependent/Initialize.h

@@ -105,6 +105,11 @@ protected:
     const char* postfixes[5];
     const char* prefixes[EbtNumTypes];
     int dimMap[EsdNumDims];
+
+private:
+    // Holds the function declarations for GL_EXT_texture_shadow_lod
+    // This extension is somewhat unique in the sense it defines overloads for built-in functions, rather than new functions.
+    TString textureShadowLodFunctions;
 };
 
 // change this back to false if depending on textual spellings of texturing calls when consuming the AST