Avoid test failures on 32-bit Cygwin in a 64-bit Cygwin environment.

Avoid test failures on 32-bit Cygwin in a 64-bit Cygwin environment.

In this situation, argv[0] is absolute, even though the program was invoked
as a file name without slashes (and thus found in $PATH).

* gettext-tools/tests/msgcmp-2: Normalize the program name better.
* gettext-tools/tests/msgcmp-3: Likewise.
* gettext-tools/tests/msgfmt-7: Likewise.
* gettext-tools/tests/msgfmt-8: Likewise.
* gettext-tools/tests/msgfmt-9: Likewise.
* gettext-tools/tests/msgfmt-10: Likewise.
* gettext-tools/tests/msgmerge-2: Likewise.
* gettext-tools/tests/msgmerge-9: Likewise.