CI: Use -fcommon to build libX11 for mingw

See discussions at xorg/lib/libx11!140
               and !913



Signed-off-by: Jeremy Huddleston Sequoia <jeremyhu@apple.com>

.gitlab-ci/cross-prereqs-build.sh

@@ -56,7 +56,9 @@ build 'https://gitlab.freedesktop.org/xorg/lib/libxcb.git' 'libxcb-1.14'
 build 'https://gitlab.freedesktop.org/xorg/lib/libxtrans.git' 'xtrans-1.4.0'
 # the default value of keysymdefdir is taken from the includedir variable for
 # xproto, which isn't adjusted by pkg-config for the sysroot
-build 'https://gitlab.freedesktop.org/xorg/lib/libX11.git' 'libX11-1.6.9' "--with-keysymdefdir=/usr/${HOST}/include/X11"
+# Using -fcommon to address build failure when cross-compiling for windows.
+# See discussion at https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/913
+CFLAGS="-fcommon" build 'https://gitlab.freedesktop.org/xorg/lib/libX11.git' 'libX11-1.6.9' "--with-keysymdefdir=/usr/${HOST}/include/X11"
 build 'https://gitlab.freedesktop.org/xorg/lib/libxkbfile.git' 'libxkbfile-1.1.0'
 # freetype needs an explicit --build to know it's cross-compiling
 # disable png as freetype tries to use libpng-config, even when cross-compiling