[master] d2d312634 Add -Wno-unknown-warning-option to libvgz cocktail, to deal with older clangs.

[Poul-Henning Kamp]

commit d2d312634d1318877d8c2c5f84b289ce44aef295
Author: Poul-Henning Kamp <phk at FreeBSD.org>
Date:   Mon Jan 30 12:07:29 2023 +0000

    Add -Wno-unknown-warning-option to libvgz cocktail, to deal with older clangs.

diff --git a/configure.ac b/configure.ac
index 93c92e29b..c21d6bf63 100644
--- a/configure.ac
+++ b/configure.ac
@@ -256,7 +256,7 @@ else
 fi
 
 # zlib-specific flags
-libvgz_extra_cflags="-Wno-error=strict-prototypes"
+libvgz_extra_cflags="-Wno-error=strict-prototypes -Wno-unknown-warning-option"
 
 dnl https://github.com/madler/zlib/issues/633
 libvgz_extra_cflags="$libvgz_extra_cflags -Wno-error=deprecated-non-prototype"