Along the way, made a change to run tool unittests when the target
"check-libc" is run by introducing a libc testsuite for tool unittests.
Reviewed By: michaelrj
Differential Revision: https://reviews.llvm.org/D93142
This adds an initial test that can serve as a basis for other tests on
wrappergen.
Reviewed By: sivachandra
Differential Revision: https://reviews.llvm.org/D92137