glob: avoid -Wattribute warnings on glibc

glob: avoid -Wattribute warnings on glibc

Colin Watson reported that some versions of gcc warn about the use
of attribute((leaf)) on static functions, since it is documented to
have an effect only on external functions.

* lib/glob.c (next_brace_sub, prefix_array, collated_compare): Use
__THROWNL, not __THROW, on static functions.
* lib/glob.in.h (__THROW): Adjust...
(__THROWNL): ...accordingly.

Signed-off-by: Eric Blake <eblake@redhat.com>