configure.ac: add option to force Check's replacement of timer_* functions
configure.ac: add option to force Check's replacement of timer_* functions

On OpenBSD 5.4 (and perhaps other BSDs) the timer_* functions
are implemented, but do nothing. Instead, they set errno to
ENOSYS (not available) and return -1. Check would check if
the timer_* functions were missing, and would use its own
replacements if they were. However, because they actually do
exist, Check does not know to replace them.

This adds another configure option, --enable-timer-replacement, which
will force Check's timer replacements instead of detecting the need.
There is still no checking if the replacements are needed or not
for OpenBSD, but at least this gives an option so check will work
properly.

git-svn-id: caee63afe878fe2ec7dbba394a86c9654d9110ca@900 64e312b2-a51f-0410-8e61-82d0ca0eb02a

svn2github/check,svn2github/check,dashaomai/check-code,dashaomai/check-code,dashaomai/check-code,svn2github/check,dashaomai/check-code,svn2github/check,svn2github/check