improvement idea: generate config.cache once by testing the libc

[rofl0r]

in the past there have been a couple cases where functionality has been added/removed from musl, which resulted in breakage from the provided config.cache file (which was not kept in tune with the musl changes).

to get rid of the need to constantly update it, we should run once a series of configure tests which generate an appropriate config.cache for the current musl version. there are of course a couple tests that can be omitted, for example the existance of all headers and functions that are required by posix and c99 must not be tested, they can be taken for granted.

[rofl0r]

seems @GregorR already created a tool to generate a local config https://github.com/GregorR/autoconf-lean/tree/master/config-site-generator