mbrtowc tests: Renumber tests. * tests/test-mbrtowc*.sh: Renamed 1 -> 2 -> 3 -> 4 -> 5 -> 1. * tests/test-mbrtowc.c: Update. * tests/test-mbrtowc-w32-*.sh: Renamed 1 -> 2 -> 3 -> 5 -> 7 -> 4 -> 6 -> 8. * tests/test-mbrtowc-w32.c: Update. * modules/mbrtowc-tests: Update.