gettext-full: link to local libxml2

gettext-full: link to local libxml2

Some users have reported that gettext builds
are attempting to link to libxml2
while it was supposed to be configured
to use it's own built-in substitute.

Configure gettext to require and link
to our local libxml2 explicitly.

Add a patch to revert upstream commit 87927a4e2
which forces libtextstyle to use the built-in libxml,
no matter what the configuration is,
making that option configurable again
after the configure script is regenerated.

Reported-by: Tianling Shen <cnsztl@immortalwrt.org>
Signed-off-by: Michael Pratt <mcpratt@pm.me>