MinGW Makefiles: do not fail if sh.exe is present in the path
If sh.exe is in the path, do not fail with MinGW compiler.
Quoting @brad.king:
The check was added only to fail early in an environment known not to work at the time. I think we can remove it since it is now blocking a valid environment.
Fixes: #19327 (closed)
Edited by Brad King