support/testing: add tests for musl and uclibc toolchains
These tests simply build a system with musl and uclibc toolchains, and boot them under qemu. It allows to minimally validate that our support for musl/uclibc external toolchains is working. We already had some tests covering glibc toolchains, so we can now easily test that all three C libraries are supported. Signed-off-by: Thomas Petazzoni <email@example.com> --- This commit is part of the series, as I've written/used those tests to validate that things are still working correctly with all of glibc, uclibc and musl toolchains.