Add support for extension GL_EXT_shader_implicit_conversions

Updated extension management in TIntermediate class.

SPIRV/GlslangToSpv.cpp

@@ -1439,7 +1439,7 @@ TGlslangToSpvTraverser::TGlslangToSpvTraverser(unsigned int spvVersion,
     // Add the source extensions
     const auto& sourceExtensions = glslangIntermediate->getRequestedExtensions();
     for (auto it = sourceExtensions.begin(); it != sourceExtensions.end(); ++it)
-        builder.addSourceExtension(it->c_str());
+        builder.addSourceExtension(it->first.c_str());
 
     // Add the top-level modes for this shader.