Fix building tests on Windows

Exclude utils/mntent.c file from the build.
Fix macro expansion in command-line on Windows

When 'shell' is set to "cmd" (which is the default).

Thanks to Sebastian Cyprych.
Remove all generated files on clean target on Win

Used to remove *.o and *.d files in src/ directory only ignoring all its
subdirectories.
Take all *.d files into account in Makefile.win

Used to take into account only *.d files in src/ directory
ignoring all its subdirectories.
Merge branch 'fix-win-macro-expansion'