Patch --enable-openmp for OSX

[Jarno Rajahalme]

Hi,

The following patch is needed for the --enable-openmp to be properly handled in 
OSX:

Btw. this patch is needed for the --enable-openmp to work on OSX:

diff -r ec3cec8277df configure.ac
--- a/configure.ac      Wed Apr 28 01:41:22 2010 -0400
+++ b/configure.ac      Mon May 03 10:51:07 2010 -0700
@@ -436,7 +436,7 @@
   [if test "$enableval" = yes; then USE_OPENMP=true; fi], [])
 if $USE_OPENMP; then
   case "$canonical_host_type" in
-    *-*-mingw* | *-*-cygwin* | *-*-gnu*)
+    *-*-mingw* | *-*-cygwin* | *-*-gnu* | *-*-darwin*)
     OCTAVE_CHECK_OPENMP(-fopenmp)
     ;;
     *-*-msdosmsvc)

Regards,

  Jarno