X86Subtarget.h: Recognize x86_64-cygwin.

In the LLVM side, x86_64-cygwin is almost as same as x86_64-mingw32.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189436 91177308-0d34-0410-b5e6-96231b3b80d8
X86JITInfo.cpp: Apply x64 version of X86CompilationCallback() to Cygwin64.

For now, (defined(X86_64_JIT) && defined(__CYGWIN__)) satisfies Cygwin64.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189437 91177308-0d34-0410-b5e6-96231b3b80d8