* Use a debug build of stage3 instead of a debug build of stage2 for
our self-hosted compiler test coverage.
* Move coverage from stage1 to stage3 for:
- building self-hosted without LLVM
- building self-hosted for 32-bit arm
- test-compiler-rt
- test-behavior
- test-std
- test-compare-output
- test-asm-link
- test-fmt