configure: If cross-compiling, assume we have working semaphores

The Asterisk 13 configure.ac checks for HAS_WORKING_SEMAPHORE but does not have
an option for cross-compiling so it fails with an exit. Since we're cross-
compiling, we can't exactly go looking for the header. The semaphore.h header
is relatively common:
* It's part of the POSIX standard
* It's part of GNU C Library
As such, we assume that it will be present when cross-compiling.

As such, this patch defaults "HAS_WORKING_SEMAPHORE" to "1" if cross-compiling
is detected.

If you're cross-compiling to a platform that doesn't support this, then make
sure you re-define this to 0.

ASTERISK-24663 #close
Reported by: abelbeck
patches:
  asterisk-13-anonymous-semaphores.patch uploaded by abelbeck (License 5903)
........

Merged revisions 430646 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@430647 65c4cc65-6c06-0410-ace0-fbb531ad65f3