libc/regex: fix internal_function declarations

libc/regex: fix internal_function declarations

Build failed with

| In file included from libc/misc/regex/regex.c:59:
| libc/misc/regex/regexec.c:315: error: conflicting types for 're_search_2_stub'
| libc/misc/regex/regexec.c:44: note: previous declaration of 're_search_2_stub' was here
| libc/misc/regex/regexec.c:358: error: conflicting types for 're_search_stub'
| libc/misc/regex/regexec.c:49: note: previous declaration of 're_search_stub' was here
.... etc

Signed-off-by: Roman I Khimov <khimov@altell.ru>
Signed-off-by: Austin Foxley <austinf@cetoncorp.com>