Linking on AIX7.2 fails:
ld: 0711-317 ERROR: Undefined symbol: .pthread_mutex_lock
ld: 0711-317 ERROR: Undefined symbol: .pthread_mutex_unlock
Bruno Haible noticed that $(LIB_MBRTOWC) and $(LIB_SETLOCALE_NULL)
expand to -lpthread on that platform, so let's add them to LDADD.
Maybe we should better depend on a 'gnulib.mk' file generated by
'gnulib-import' in the long run, but let's fix this issue with the
simpler solution for now.
* find/Makefile.am (LDADD): Add $(LIB_SETLOCALE_NULL) and $(LIB_MBRTOWC).
* locate/Makefile.am (LDADD): Likewise.
* xargs/Makefile.am (LDADD): Likewise.
* lib/Makefile.am (regexprops_LDADD): Add definition.