[pango] Disable -Werror=undef

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 0f75002573abfe6494efec5973d07d23167da579
Author: Michael Catanzaro <mcatanzaro igalia com>
Date:   Mon Feb 12 12:19:41 2018 -0600

    Disable -Werror=undef

 meson.build |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/meson.build b/meson.build
index be63612..3218550 100644
--- a/meson.build
+++ b/meson.build
@@ -97,7 +97,7 @@ elif cc.get_id() == 'gcc' or cc.get_id() == 'clang'
     '-Werror=pointer-to-int-cast',
     '-Werror=empty-body',
     '-Werror=write-strings',
-    '-Werror=undef',
+    '-Wundef', # FIXME: https://bugzilla.gnome.org/show_bug.cgi?id=792481
   ]
 
   if host_system == 'windows'