grep-2.5.4-20080209b compilation warnings

[Karl Berry]

I tried compiling the new test release at
http://alpha.gnu.org/gnu/grep/grep-2.5.4-20080209b.tar.gz with gcc 4.2.3
on CentOS 5.  There were two compilation warnings (which were repeated
for each search.c compilation, of course; I'll spare you the repetitions).

In file included from ../lib/regex.h:2,
                 from search.c:37:
../lib/posix/regex.h:536:1: warning: "__restrict_arr" redefined
In file included from /usr/include/features.h:329,
                 from /usr/include/sys/types.h:27,
                 from search.c:25:
/usr/include/sys/cdefs.h:299:1: warning: this is the location of the previous 
definition

search.c: In function 'check_multibyte_string':
search.c:169: warning: passing argument 1 of 'wcrtomb' discards qualifiers from 
pointer target type