[xalan-c] Use CMake build system, enables linux/mac build

[seanwarren]

This PR updates the xalan-c port to uses the CMake build written by @rleigh-codelibre (see https://jira.apache.org/jira/browse/XALANC-776).

This enables building xalan-c on mac and linux under vcpkg.

Two patches (#8 and #9) have been pulled directly into the port.

[rleigh-codelibre]

While I'm happy for this to be included, please note that it has not had the same level of rigourous testing which the Xerces-C++ CMake build has had. Please do check that the library names and exported ABI is identical to the existing msbuild project and solution file output before making the change, or else it could result in breakage.

In the next few months, I should be accepted onto the PMC for Xalan, at which point I'll be able to merge the entire patchset, plus the CMake build, and make a new upstream release. This will permit these patchset to be dropped.

Thanks,
Roger

[seanwarren]

Hi Roger, if there is a plan for these changes to be merged upstream it's probably worth waiting for that.

Cheers
Sean