gettext: beat library detection into shape

gettext: beat library detection into shape

For reasons I can't explain gettext uses several hundred lines of convoluted m4
to find the paths to a library.

If we don't tell it where to find a library it will hunt around and potentially
have host contamination as /usr/lib on the host is explicitly searched.

If we tell it the prefix to a library then we get bad RPATHs in the binaries
(such as /usr/lib/../lib), and the search assumes that it knows best about what
the library directories are under that prefix (even when it's wrong).

So, replace the lookup where possible with pkg-config calls (libxml2, glib,
libcroco).  libunistring doens't have a pkgconfig file so just don't use the
system libunistring: the library is tiny anyway.

(From OE-Core rev: 1ff35fbbdd50660b86f8e254685ae0c8338b6e11)

(From OE-Core rev: e6c0f8eddf8ff4a6132934a69e0f3450d4843ece)

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>