Log Message:
ffmpeg[7,5,4,3]: Fix build on NetBSD/mips64

The assembler code uses MIPS IV instructions while the NetBSD
toolchain defaults to MIPS III. This renders the package
uncompilable.

ffmpeg2 is unaffected, ffmpeg6 already has the fix applied.

XXX unsure if we're running mips64 on any MIPS III processors by
default, but this is at least better than the package failing on
every mips64 processor