Import patch from PR 262877 to enable symbol versioning

Import following upstream commits:
5c71ada83acf30dc7e8ca8fca1f025c7dd014447 (partially)
141d784ecffaf00f152f8a7c627e72f72d398f34 (replaces local patch)
6d10df7c5c6a098078db8a7649d5d9a1f820d9cd (replaces local patch)
f2987a295ff847ecb2a6a3eae1a271c9a64255b6
94ac5e61f399759a5463c0505099222ed8f13a82 (fixes PR 263094)
4d98f6f9c5fb29c624e469665e4fc349d4057914

Add alternative variant of upstream commit (in Makefile)
28d0399682027cc65dd17ac675bde85a11e5a01e (remove xsa file)

Changes:
CFLAGS and INCLUDEDIR no longer refers to ${PREFIX}/include 
in bin/xml2-config , libxml-2.0.pc or lib/xml2Conf.sh (fixes PR 262824)