testsuite tests for Cygwin<->Win32 process interaction

[Jeremy Drake]

I would like to add tests of invoking non-Cygwin processes using
posix_spawn and making sure their stdin/out/err and cwd are as expected.
I see that there is a mingw directory for building with the cross-mingw
compiler, and I could make a test child process built through that which
uses GetFileInformationByHandleEx and GetCurrentDirectoryW.

Can I be assured that when the winsup.api tests run that the mingw tests
have already been built, or do I need some sort of dependency declared in
the Makefile.am?  How should the winsup.api test find the mingw test exe?
Should I figure out what the cwd of the test run from the testsuite is and
just use a relative path?  dladdr an address in the exe and use the
returned path to the exe to construct a path to the mingw exe?