1 files changed, 20 insertions, 0 deletions
diff --git a/m4/jh-add-cflag.m4 b/m4/jh-add-cflag.m4
new file mode 100644
index 0000000..75fa78c
--- /dev/null
+++ b/m4/jh-add-cflag.m4
@@ -0,0 +1,20 @@
+dnl JH_ADD_CFLAG(FLAG)
+dnl checks whether the C compiler supports the given flag, and if so, adds
+dnl it to $CFLAGS.  If the flag is already present in the list, then the
+dnl check is not performed.
+AC_DEFUN([JH_ADD_CFLAG],
+[
+case " $CFLAGS " in
+*@<:@\	\ @:>@$1@<:@\	\ @:>@*)
+  ;;
+*)
+  save_CFLAGS="$CFLAGS"
+  CFLAGS="$CFLAGS $1"
+  AC_MSG_CHECKING([whether [$]CC understands $1])
+  AC_TRY_COMPILE([], [], [jh_has_option=yes], [jh_has_option=no])
+  AC_MSG_RESULT($jh_has_option)
+  if test $jh_has_option = no; then
+    CFLAGS="$save_CFLAGS"
+  fi
+  ;;
+esac])