Now that -mstack-probe-size is piped through to the backend via the function
attribute as on Windows x86, honour the value to permit handling of non-default
values for stack probes. This is needed /Gs with the clang-cl driver or
-mstack-probe-size with the clang driver when targeting Windows on ARM.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@227667 91177308-0d34-0410-b5e6-96231b3b80d8
