[Toybox] macOS test sitrep

[enh]

since i'm out all week next week and actively trying to avoid breaking
anything, today seemed like a good time to go through all the mac test
failures.

only two of the patches (the device major/minor one and the setlocale
one) revealed actual bugs in toybox on mac. the rest were all working
around linux/mac differences.

if you apply all nine or so patches, you'll be running _more_ tests on
macOS than before, and with only two remaining failures: two of the
printf tests fail because the mac is still on bash 3.2. i can send you
a patch for that (similar to the iconv one), or we can just assume
that toysh will be along before too long.

i have no way to run mac tests in automation anyway, so i don't care either way.

actually, since i have the patch anyway (to check i'd really
understood the problem) i'll send it out and you can either commit it
or not. with that, `make test` has no failures for me on macOS
10.14.6.