[clang] [clang][ssaf] Fix building on gcc-7 and MinGW/Cygwin (PR #181812)

[Balázs Benics via cfe-commits]

steakhal wrote:

Alright, it's been an hour. I think I'll just merge this to see if the bots will be fixed.

https://github.com/llvm/llvm-project/pull/181812