ges: fix API export/import and 'inconsistent linkage' on MSVC

Submitted by Tim Müller @tpm

Link to original bug (#797197)

Description

Created attachment 373746
ges fix API export/import and 'inconsistent linkage' on MSVC

Putting patch here for now, since I haven't been able to actually test it with MSVC yet (need to add libxml2 wrap to gst-build I guess).

"Should be ok" of course, but didn't just want to push it.

Patch 373746, "ges fix API export/import and 'inconsistent linkage' on MSVC":
0001-libs-fix-API-export-import-and-inconsistent-linkage-.patch