Problem:

alloc.c: In function `ap_cleanup_alloc':
alloc.c:524: warning: statement with no effect
alloc.c:525: warning: statement with no effect

Reason:
We have the declaration "API_EXPORT(void) ap_destroy_mutex(mutex *mutex_id);",
in case of multithreading, so ap_destroy_mutex() should not be defined as
"(0)" in case of no multithreading, because "(0);" causes the above warnings.

Fix:
ANSI C allows empty statements, so let ap_destroy_mutex() expand to not
nothing instead.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@85840 13f79535-47bb-0310-9956-ffa450edef68