Support cross-compiling

The strftime configure test uses AC_TRY_RUN while only defining the first two arguments. This fails by default when cross-compiling:

checking for working mmap... (cached) yes
configure: error: in `/var/tmp/portage/xfce-base/exo-4.16.0/work/exo-4.16.0':
configure: error: cannot run test program while cross compiling

Specifying the fourth argument would allow it to proceed:

--- a/configure.ac
+++ b/configure.ac
@@ -151,6 +151,7 @@
   }
 ], [
   AC_DEFINE([HAVE_STRFTIME_EXTENSION], 1, [Define if strftime supports %E and %O modifiers.])
+],,[AC_MSG_WARN([skipping strftime test due to cross-compiling])
 ])
 
 dnl ******************************

Could it do this or maybe be rewritten to use a cache variable to allow specifying the behavior of the target system?