Enable enumeration types with a fixed underlying type, e.g.,

Enable enumeration types with a fixed underlying type, e.g.,

  enum X : long { Value = 0x100000000 };

when in Microsoft-extension mode (-fms-extensions). This (now C++0x)
feature has been supported since Microsoft Visual Studio .NET 2003.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@126243 91177308-0d34-0410-b5e6-96231b3b80d8