[Sema] Allow conversion between long double and __float128.

We should only ban this if long double is a double double. x86's 80 bit
long double is fine and supported by the backend.

llvm-svn: 322779
diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
index e7eb309..b80f14d 100644
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -1764,8 +1764,8 @@
                                    (FromType == S.Context.LongDoubleTy &&
                                     ToType == S.Context.Float128Ty));
       if (Float128AndLongDouble &&
-          (&S.Context.getFloatTypeSemantics(S.Context.LongDoubleTy) !=
-           &llvm::APFloat::IEEEdouble()))
+          (&S.Context.getFloatTypeSemantics(S.Context.LongDoubleTy) ==
+           &llvm::APFloat::PPCDoubleDouble()))
         return false;
     }
     // Floating point conversions (C++ 4.8).