hpc
replace argp with something more portable
We use GNU argp to parse command line arguments. This is a GNU extension and only present in glibc. Building with another libc means that argp must be supplied externally (see PR #1258), but this appears to not be well supported. While there is an Alpine package, it depends on an apparently-unmaintained extraction of the argp code from glibc dated 2004.
An alternative is getopt_long(3), which is also a GNU extension but does appear to be supported by musl.
There is a tool called Gengetopt that provides a DSL compiled to getopt_long(3) calls and supporting code.
One thing we currently rely on from argp is that in ch-run --set-env FOO -- ..., it knows FOO is the image name, not the argument to --set-env. getopt_long(3) uses a greedy algorithm and thus AFAICT will get this wrong.
The argp-standalone maintained at:
https://github.com/ericonr/argp-standalone
is what Gentoo uses and seems to be slightly better maintained than what Alpine is using right now. However, the general argument to switch to something more portable holds.
