Use c-ctype.h (not safe-ctype.h) in gdb

This changes gdb and related programs to use the gnulib c-ctype code
rather than safe-ctype.h.  The gdb-safe-ctype.h header is removed.

This changes common-defs.h to include the c-ctype header, making it
available everywhere in gdb.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33217
Approved-By: Simon Marchi <simon.marchi@efficios.com>