When building on Windows, we must link against `Bcrypt` to satisfy the
use of `BCryptGenRandom`. Add this to the link interface in CMake to
allow use of libxml2 as a static library.
If they were required when building libxml2 then they will also be
required when statically linking against it. Failing to find them will
just lead to undefined references later so detect this early.
* add libxml2-config.cmake.in template
* configure.ac: add libxml2-config.cmake.in to the configured file list
* Makefile.am: install libxml2-config.cmake under ${libdir}/cmake/libxml2
Signed-off-by: Samuel Martin <s.martin49@gmail.com>
