ax_prog_flex.m4: Merge upstream OpenBSD fixes.

Merge the following upstream autoconf-archive patches.

ax_prog_flex: change grep syntax to accept e.g. "flex.real" in case a wrapper or symlink is used.
AX_PROG_FLEX: avoid use of grep empty string escape extension (fix for OpenBSD)
AX_PROG_FLEX: Also accept gflex.

Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Jonathan Gray <jsg@openbsd.org>
1 file changed