nstrftime tests: Test in the UTF-8 environment on native Windows. Prompted by <https://debbugs.gnu.org/79296>. * tests/test-nstrftime-w32utf8.sh: New file. * tests/test-nstrftime-w32utf8.c: New file. * modules/nstrftime-tests (Files): Add them. Add windows-utf8.rc, windows-utf8.manifest, m4/windows-rc.m4. (configure.ac): Invoke gl_WINDOWS_RC. (Makeile.am): Arrange to build test-nstrftime-w32utf8 and run test-nstrftime-w32utf8.sh.