Use consistent style to check DEBUG macro in regex_internal.c
The DEBUG macro is checked using both #if and #ifdef in
regex_internal.c. Make this consistent with mktime, where we use "#if
defined DEBUG && DEBUG", to be compatible with gnulib as well as glibc
style.
regex: Make #if/#ifdef usage consistent for DEBUG
* lib/regex_internal.c: Use "#if defined DEBUG && DEBUG" instead
of the inconsistent usage of #if and #ifdef as that works with
both Glibc and Gnulib's style.