Log Message:
libxslt: fix libxml2 detection with libxml2 >= 2.9.11

xml2-config from libxml2 >= 2.9.11 now exits with non-zero status
for invalid arguments. libxslt called xml2-config with the invalid
`print` option to probe for its existence, so with new libxml2 it
now skipped detection via xml2-config entirely causing a build
failure.

Apply upstream patch to correct this invalid xml2-config usage.