This doesn't feel as natural, but is more consistent with the boolean options
which require true/false, and allows setting of options without knowing of
which type the option is.
This is a very straightforward conversion of the rules in Makefile.am.
Generated objects (on arm64) are identical.
The only difference in executed commands is that automake uses ld -m
elf_x86_64, without us specifying the -m option anywhere. I suspect that
using the default for the given linker should be OK, so it's fine to just
skip it.
