microbench: Add fallback to gettimeofday()

Some operating systems such as OS/2 don't have any of the CLOCK* API
functions so add gettimeofday() as a fallback.

Signed-off-by: Dave Yeo <dave.r.yeo@gmail.com>
Signed-off-by: Erik de Castro Lopo <erikd@mega-nerd.com>
diff --git a/configure.ac b/configure.ac
index 915869b..b577248 100644
--- a/configure.ac
+++ b/configure.ac
@@ -371,6 +371,11 @@
 AH_TEMPLATE(FLAC__HAS_DOCBOOK_TO_MAN, [define if you have docbook-to-man or docbook2man])
 fi
 
+AC_CHECK_LIB(rt, clock_gettime, have_clock_gettime=yes)
+if test x$have_clock_gettime = xyes; then
+        AC_DEFINE(HAVE_CLOCK_GETTIME)
+fi
+
 # only matters for x86
 AC_CHECK_PROGS(NASM, nasm)
 AM_CONDITIONAL(FLaC__HAS_NASM, test -n "$NASM")