Objective C/MinGW: Use functions in libobjc2 for exception handling

The current implementation uses functions which are declared in the
C++ standard library to throw and catch excpetions.
This requires linking with said library, which most toolchains do not
do natively.

clang/lib/CodeGen/CGException.cpp

@@ -159,7 +159,7 @@ static const EHPersonality &getObjCPersonality(const TargetInfo &Target,
     return EHPersonality::NeXT_ObjC;
   case ObjCRuntime::GNUstep:
     if (T.isOSCygMing())
-      return EHPersonality::GNU_CPlusPlus_SEH;
+      return EHPersonality::GNU_ObjC_SEH;
     else if (L.ObjCRuntime.getVersion() >= VersionTuple(1, 7))
       return EHPersonality::GNUstep_ObjC;
     [[fallthrough]];
@@ -216,7 +216,7 @@ static const EHPersonality &getObjCXXPersonality(const TargetInfo &Target,
     return getObjCPersonality(Target, L);
 
   case ObjCRuntime::GNUstep:
-    return Target.getTriple().isOSCygMing() ? EHPersonality::GNU_CPlusPlus_SEH
+    return Target.getTriple().isOSCygMing() ? EHPersonality::GNU_ObjC_SEH
                                             : EHPersonality::GNU_ObjCXX;
 
   // The GCC runtime's personality function inherently doesn't support

clang/lib/CodeGen/CGObjCGNU.cpp

@@ -829,12 +829,12 @@ class CGObjCGNUstep : public CGObjCGNU {
       // If we're in ObjC++ mode, then we want to make
       llvm::Type *VoidTy = llvm::Type::getVoidTy(VMContext);
       if (usesCxxExceptions) {
-        // void *__cxa_begin_catch(void *e)
-        EnterCatchFn.init(&CGM, "__cxa_begin_catch", PtrTy, PtrTy);
-        // void __cxa_end_catch(void)
-        ExitCatchFn.init(&CGM, "__cxa_end_catch", VoidTy);
-        // void objc_exception_rethrow(void*)
-        ExceptionReThrowFn.init(&CGM, "__cxa_rethrow", PtrTy);
+        // void *objc_begin_catch(void *e)
+        EnterCatchFn.init(&CGM, "objc_begin_catch", PtrTy, PtrTy);
+        // void objc_end_catch(void)
+        ExitCatchFn.init(&CGM, "objc_end_catch", VoidTy);
+        // void objc_exception_rethrow(void)
+        ExceptionReThrowFn.init(&CGM, "objc_exception_rethrow", VoidTy);
       } else if (usesSEHExceptions) {
         // void objc_exception_rethrow(void)
         ExceptionReThrowFn.init(&CGM, "objc_exception_rethrow", VoidTy);