chelf: init at 0.2.2

Utility for changing default thread stack size
(via PT_GNU_STACK program header)
as supported by musl 1.1.21+.

patchelf for default thread stack size :).

This makes it possible to use a larger value
without changing the source, which is preferred
but may be awkward or otherwise undesirable in some cases.

The value can also be set via LDFLAGS with some linkers,
such as with GNU ld using "-Wl,-z,stack-size=N".

See:
https://git.musl-libc.org/cgit/musl/commit/?id=7b3348a98c139b4b4238384e52d4b0eb237e4833