EE/Interpreter/ExternalFunctions.cpp: Prune "C" linkage to suppress warnings with -Wreturn-type (and MSC's w4190).

In historical reason, Interpreter's external entries had prefix "lle_X_" as C linkage, even for well-known entries in EE/Interpreter.
Now, at least on ToT, they are resolved via FuncNames[] mapper.
We will not need their symbols are expected to be exported any more.

Clang r150128 has introduced the warning <"%0 has C-linkage specified, but returns user-defined type %1 which is incompatible with C">.

llvm-svn: 151312

llvm/lib/ExecutionEngine/Interpreter/ExternalFunctions.cpp

@@ -297,17 +297,6 @@ GenericValue Interpreter::callExternalFunction(Function *F,
 //  Functions "exported" to the running application...
 //
 
-// Visual Studio and Clang warn about returning GenericValue in extern "C" linkage
-#ifdef _MSC_VER
-    #pragma warning(disable : 4190)
-#endif
-#ifdef __clang__
-    #pragma clang diagnostic push
-    #pragma clang diagnostic ignored "-Wreturn-type-c-linkage"
-#endif
-
-extern "C" {  // Don't add C++ manglings to llvm mangling :)
-
 // void atexit(Function*)
 GenericValue lle_X_atexit(FunctionType *FT,
                           const std::vector<GenericValue> &Args) {
@@ -473,17 +462,6 @@ GenericValue lle_X_fprintf(FunctionType *FT,
   return GV;
 }
 
-} // End extern "C"
-
-// Done with externals; turn the warning back on for Clang and Visual Studio
-#ifdef __clang__
-    #pragma clang diagnostic pop
-#endif
-#ifdef _MSC_VER
-    #pragma warning(default: 4190)
-#endif
-
-
 void Interpreter::initializeExternalFunctions() {
   sys::ScopedLock Writer(*FunctionsLock);
   FuncNames["lle_X_atexit"]       = lle_X_atexit;