fix bug for o_direct

configure.ac

@@ -137,9 +137,12 @@ case "$target" in
 esac
 AM_CONDITIONAL([STARPU_HAVE_WINDOWS], [test "x$starpu_windows" = "xyes"])
 
-case ${target_os} in linux*)
-  AM_CONDITIONAL(STARPU_LINUX_SYS, test 1 = 1)
+case "$target_os" in
+*linux*)
+  starpu_linux=yes
+  ;;
 esac
+AM_CONDITIONAL(STARPU_LINUX_SYS, [test "x$starpu_linux" = "xyes"])
 
 # on Darwin, GCC targets i386 by default, so we don't have atomic ops
 AC_CHECK_SIZEOF([void *])