Enable limited testing in Makefile.msft without Cygwin

Enable limited testing in Makefile.msft without Cygwin
(Cherry-pick commit 18a05e9 from 'master' branch.)

New target "check-noautogen" is introduced in Makefile.msft to build and
run only test_malloc and test_stack (which do not need test code
auto-generation by sed).

* src/Makefile.msft: Refine comment about tests execution; add comment
about "check-noautogen" target.
* src/Makefile.msft (check): Add dependency on check-noautogen;
move test_malloc and test_stack to check-noautogen.
* src/Makefile.msft (check-noautogen): New target (executes test_malloc
and test_stack only).