Two macOS fixes

[John Klos <john%klos.com@localhost>]

Hi,

I see that benchmarks/nbench won't compile on macOS because it can't link 
-lcrt0.o. Would the simplest fix be to just build it statically, with 
"BUILDLINK_TRANSFORM+=rm:-static"?

Also, I noticed that multimedia/ffmpeg6 has 
"LDFLAGS.Darwin+=-Wl,-ld_classic", but ffmpeg6 won't compile with this 
("ld: library not found for -ld_classic"). Was this perhaps needed for 
older versions of macOS?

Thanks,
John