Remove -fseh-exceptions in favor of checking the triple

This option was misleading because it looked like it enabled the
language feature of SEH (__try / __except), when this option was really
controlling which EH personality function to use. Mingw only supports
SEH and SjLj EH on x86_64, so we can simply do away with this flag.

llvm-svn: 221963

clang/lib/Frontend/InitPreprocessor.cpp

@@ -572,8 +572,6 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
     Builder.defineMacro("__GXX_RTTI");
   if (LangOpts.SjLjExceptions)
     Builder.defineMacro("__USING_SJLJ_EXCEPTIONS__");
-  if (LangOpts.SEHExceptions)
-    Builder.defineMacro("__SEH__");
 
   if (LangOpts.Deprecated)
     Builder.defineMacro("__DEPRECATED");