These targets don't actually cross-compile -- they try to pull some
objects out of the host's /lib/libc.a, /lib/libm.a, and /lib/crt0.o
directly and merge them into newlib's own libraries. This is hard
to keep working and impossible to test. Considering the vintage of
such targets, and gcc dropping them many many years ago, drop them
from newlib too. This will make cleaning up the build a lot easier.
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