Fix build with glib 2.68.3

Obtained from [1] via [2].

[1] https://aur.archlinux.org/cgit/aur.git/tree/xiphos-glibc.patch?h=xiphos
[2] https://github.com/crosswire/xiphos/issues/1083

--- cmake/config.h.cmake.in.orig	2021-07-24 06:17:00 UTC
+++ cmake/config.h.cmake.in
@@ -65,3 +65,5 @@
 
 
 #endif
+
+#define GLIB_VERSION_MIN_REQUIRED (GLIB_VERSION_2_26)