Detect and use xsltCleanupGlobals when available

This introduces usage of an additional libxslt cleanup function,
xsltCleanupGlobals, when the configure script detects that it is
available. Early versions of the library did not include this function.

(closes issue ASTERISK-22570)
Reported by: Corey Farrell
Patches:
    xsltCleanupGlobals.patch uploaded by Corey Farrell (License 5909)
........

Merged revisions 400384 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@400385 f38db490-d61c-443f-a65b-d21fe96a405b