This change addresses an issue where ksh hangs when the number of jobs exceeds `2^15 - 1` (32767), which is the maximum value for a `short`.

src/cmd/INIT/mamake.c:
- Option -V: Silence an annoying gcc warning by checking the return
  value of write(2). It's kind of pointless just for printing the
  version, but on gcc, (void)write will not suppress the warning.
  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66425

src/cmd/ksh93/tests/arith.sh:
- The Gentoo ebuild explicitly unsets A, which is apparently
  exported in their environment, killing the arith.sh tests.
  So this unsets it in the script.
  https://gitweb.gentoo.org/repo/gentoo.git/tree/app-shells/ksh/ksh-1.0.9.ebuild

README.md, src/cmd/ksh93/README:
- Fix typos.