Windows itanium targets the MSVCRT, and the stack probe symbol is provided by
MSVCRT. This corrects the emission of stack probes on i686-windows-itanium.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222439 91177308-0d34-0410-b5e6-96231b3b80d8