fix "lua_vmprep.c:29:6: warning: no previous prototype for ‘ap_lua_init_mutex’...

fix "lua_vmprep.c:29:6: warning: no previous prototype for ‘ap_lua_init_mutex’ [-Wmissing-prototypes]"


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1369800 13f79535-47bb-0310-9956-ffa450edef68