configure.ac: fix detection

configure.ac

@@ -2008,13 +2008,12 @@ AC_DEFUN([IS_SUPPORTED_CFLAG],
 		),
 		[
 			GLOBAL_AM_CFLAGS="$GLOBAL_AM_CFLAGS $1"
-			if test "$2" != ""; then
-			    AC_DEFINE("$2", [], Define this when option $1 available.)
-			fi
 			AC_MSG_RESULT(yes)
+			option_available=1
 		],
 		[
 			AC_MSG_RESULT(no)
+			option_available=0
 		]
 	)
 	CFLAGS="$SAVED_CFLAGS"
@@ -2144,7 +2143,8 @@ fi
 AM_CONDITIONAL([STARPU_OPENMP], [test "x$enable_openmp" = "xyes"])
 AC_MSG_RESULT($enable_openmp)
 
-IS_SUPPORTED_CFLAG(-fopenmp, STARPU_HAVE_OPENMP)
+IS_SUPPORTED_CFLAG(-fopenmp)
+AM_CONDITIONAL([STARPU_HAVE_OPENMP],[test "$option_available" = "1"])
 
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