Replace GNU testsuite

[inkydragon]

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

• Setup coverage ci test: add target to gen coverage report #295
• Test with qemu: cover arm, aarch64, ppc64le, mips, riscv64, s390x CI: Setup cross build test #296
  https://github.com/libuv/libuv/blob/3b6a1a14caeeeaf5510f2939a8e28ed9ba0ad968/.github/workflows/CI-unix.yml#L97
• fix loongson64 cross build?
• Add musl-libc test test: add musl-libc testsuite #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.