contrib: Update fribidi url to use GitHub tarball.

contrib: Update fribidi url to use GitHub tarball.

fribidi.org is gone. The official release archive we were using is gone. Only release tags on GitHub remain, and they are not direct replacements for the proper release archives we were using previously.

Some changes were necessary for compilation from source, namely:

- Removal of an ugly hack that resulted in configure being run more than once. Apparently the same fix is already upstream https://github.com/fribidi/fribidi/commit/0efbaa9052320a951823a6e776b30a580e3a2b4e
- Modification of Makefile.am to avoid building the doc subdirectory, since this will fail wherever c2man isn't available such as on Mac. We don't need these docs
- Modification of gen.tab/Makefile.in to use the host compiler when cross-compiling. This cannot be done as a normal patch since Makefile.in is generated in the bootstrap phase. This is an open issue upstream: https://github.com/fribidi/fribidi/issues/7

This is all a good lesson on the importance of maintaining urls. I'm still a bit stunned a widely used GNU project would shutter its domain and release archive.