This is a set of forward ports (cherry-picks) from 8.10

- a7d22795 [ci] Add support for building on aarch64-darwin
- 5109e87e [testlib/driver] denoise
- 307d3494 [ci] default value for CONFIGURE_ARGS
- 10a18cb4 [testsuite] mark ghci056 as fragile
- 16c13d5a [ci] Default value for MAKE_ARGS
- ab571457 [ci/build] Copy config.sub around
- 251892b9 [ci/darwin] bump nixpkgs rev
- 5a6c36ec [testsuite/darwin] fix conc059
- aae95ef0 [ci] add timing info
- 3592d110 [Aarch64] No div-by-zero; disable test.
- 57671071 [Darwin] mark stdc++ tests as broken
- 33c4d497 [testsuite] filter out superfluous dylib warnings
- 4bea83af [ci/nix-shell] Add Foundation and Security
- 63455300 [testsuite/json2] Fix failure with LLVM backends
- c3944bc8 [ci/nix-shell] [Darwin] Stop the ld warnings about libiconv.
- b821fcc7 [testsuite] static001 is not broken anymore.
- f7062e1b [testsuite/arm64] fix section_alignment
- 820b0766 [darwin] stop the DYLD_LIBRARY_PATH madness
- 07b1af03 [ci/nix-shell] uniquify NIX_LDFLAGS{_FOR_TARGET}

As well as a few additional fixups needed to make this block compile:
- Fixup all.T
- Set CROSS_TARGET, BROKEN_TESTS, XZ, RUNTEST_ARGS, default value.
- [ci] shell.nix bump happy