X86: Disable IsLegalToCallImmediateAddr for Win32

WinCOFF cannot form PC relative relocations to support absolute
MCValues.  We should reenable this once WinCOFF supports emission of
IMAGE_REL_I386_REL32 relocations.

This fixes PR19272.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205058 91177308-0d34-0410-b5e6-96231b3b80d8