Replace GNU testsuite

[inkydragon]

Maybe we can use tests from musl libc: https://wiki.musl-libc.org/libc-test.html which is MIT license.

• [x] Setup coverage ci #295
• [x] Test with qemu: cover arm, aarch64, ppc64le, mips, riscv64, s390x #296 https://github.com/libuv/libuv/blob/3b6a1a14caeeeaf5510f2939a8e28ed9ba0ad968/.github/workflows/CI-unix.yml#L97
• [ ] fix loongson64 cross build?
• [ ] Add musl-libc test #298
• [ ] test run libc-test by default The GNU testsuit test code is kept, but not used by default, and could probably be removed after some more time.

[ViralBShah]

It is possibly also a lot more comprehensive. Good to have it.