fix(gen): strip src/ prefix from linux/macosx source globs (undefined avutil_version)

compress_sources kept the sources.txt 'src/' prefix (linux/macosx snapshots
carry it; windows doesn't), producing '*/src/libavcodec/...' globs that match
nothing → empty compat.ffmpeg → undefined avutil_version/avcodec_* at test link.
Strip src/ + drop the stray -Pconfig.asm artifact line. Verified: linux 2281 /
macosx 2091 / windows 2283 sources, all symbol-defining files (utils.c,
allcodecs.c, allformats.c) covered per OS.

Author: Sunrisepeak