[compiler-rt] [compiler-rt] Allow to build on CYGWIN (PR #66348)

[Carlo Bramini via llvm-commits]

carlo-bramini wrote:

> Thanks, this looks good to me. For context; are you building compiler-rt with the default GCC of cygwin, or with clang targeting cygwin?

I'm using GCC version 11.4.0, same toolchain version for both CYGWIN posix applications and MinGW-w64 cross compilers.

https://github.com/llvm/llvm-project/pull/66348