x264 and ffmpeg RPM conflicts

[Antoine Martin]

Discovered as part of #1462, trying to inspect the 10-bit x264 stream.

Despite being located in our private library directory, because of some automagic during rpmbuild, our RPMs claim to provide a specific version of libx264.so and the ffmpeg shared libraries:

rpm -q --provides ./x264-xpra-20190929-1.fc32.x86_64.rpm
libx264.so.157()(64bit)
x264-xpra = 20190929-1.fc32
x264-xpra(x86-64) = 20190929-1.fc32

$ rpm -q --provides ./ffmpeg-xpra-4.2.2-2.fc32.x86_64.rpm
ffmpeg-xpra = 4.2.2-2.fc32
ffmpeg-xpra(x86-64) = 4.2.2-2.fc32
libavcodec.so.58()(64bit)
libavcodec.so.58(LIBAVCODEC_58)(64bit)
libavfilter.so.7()(64bit)
libavfilter.so.7(LIBAVFILTER_7)(64bit)
libavformat.so.58()(64bit)
libavformat.so.58(LIBAVFORMAT_58)(64bit)
libavutil.so.56()(64bit)
libavutil.so.56(LIBAVUTIL_56)(64bit)
libpostproc.so.55()(64bit)
libpostproc.so.55(LIBPOSTPROC_55)(64bit)
libswresample.so.3()(64bit)
libswresample.so.3(LIBSWRESAMPLE_3)(64bit)
libswscale.so.5()(64bit)
libswscale.so.5(LIBSWSCALE_5)(64bit)

This then conflicts with other repositories that provide x264 and / or ffmpeg.
Some tools may complain that one of the libraries is missing, since we do not pollute the LD_LIBRARY_PATH.
It gets worse when the library number changes.

[Antoine Martin]

Should be fixed in r26905.

New RPMs will need to be uploaded to stable.