Test that c_iscntrl agrees with iscntrl, etc. Suggested by Daniel Richard G. in: http://lists.gnu.org/archive/html/bug-gnulib/2015-09/msg00034.html * modules/c-ctype-tests (Depends-on): Add ctype. * tests/test-c-ctype.c: Include <ctype.h>. (NCHARS): New constant. (test_agree_with_C_locale): New function. (main): Use it. (test_all): Use named constants.