Fix one compile error when configuring for debug build (`-O0 -g3`)

When doing a debug compile using the below commands the build fails:

    make clean
    ./configure CFLAGS='-g3 -O0'
    make

The error output is

    audstrings.c: In function ‘filename_to_uri’:
    audstrings.c:147:9: warning: implicit declaration of function ‘setlocale’
    [-Wimplicit-function-declaration]
    audstrings.c:147:42: error: ‘LC_ALL’ undeclared (first use in this function)
    audstrings.c:147:42: note: each undeclared identifier is reported only once for
    each function it appears in
    audstrings.c: In function ‘uri_to_filename’:
    audstrings.c:189:42: error: ‘LC_ALL’ undeclared (first use in this function)
    Failed to compile audstrings.c (lib)!
    make[5]: *** [audstrings.lib.o] Error 1
    make[4]: *** [all] Error 2
    make[3]: *** [subdirs] Error 2
    make[2]: *** [all] Error 2
    make[1]: *** [subdirs] Error 2
    make: *** [all] Error 2

There's no difference in output between `./configure` and `./configure
CFLAGS='-g3 -O0'`. Neither is there one between the resulting files in the
directory. Seems to be a library problem somewhere or this simple fix.

Tested on Fedora 18.