Correct OS conditionals following r204977 and r204978.

Previously, MinGW OS was Triple::MinGW and Cygwin was Triple::Cygwin
and now it is Triple::Win32 with Environment being GNU or Cygwin.
So,

  TheTriple.getOS() == Triple::Win32 
  
is replaced by

  TheTriple.isWindowsMSVCEnvironment()

and

  (TheTriple.getOS() == Triple::MinGW32 || TheTriple.getOS() == Triple::Cygwin)
  
is replaced by

  TheTriple.isOSCygMing()




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205170 91177308-0d34-0410-b5e6-96231b3b80d8
Try to fix MSan bootstrap bot: make ARM64Disassembler::getInstruction() always initialize Size argument.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205171 91177308-0d34-0410-b5e6-96231b3b80d8