Like in the recent commit, also change the following variables to follow
the renaming done in gnulib:
- LIB_SETLOCALE_NULL -> SETLOCALE_NULL_LIB,
- LIB_MBRTOWC -> MBRTOWC_LIB,
- LIB_EACCESS -> EUIDACCESS_LIBGEN.
* find/Makefile.am (LDADD): Change as described above.
* lib/Makefile.am: Likewise.
* locate/Makefile.am: Likewise.
* xargs/Makefile.am: Likewise.