Support shared lib for libtinyxml2.

libtinyxml2 is linked by bluetooth.default (/system/bt/main/Android.mk)
and many vendors' components.

So using it as shared lib will be good for easy update and size
reduction.

Test: building succeeded, and the image was tested on angler.
Bug: 33056637
Change-Id: I2b66bdadf184ef1a4b765b8ddca585ec1042d185