Draft: RISCV64 NCG based on GHC 9.10

To keep up with GHC development and to gain benefits of later developments (e.g. more tests), base the RISCV64 NCG efforts on ghc-9.10 (release branch.) This is still WIP (some new MachOps aren't implemented yet, so expect panics.)

The patches will land on master. ghc-9.10 has been chosen because it's more stable.

Tickets: #16783 (closed) , #23179 (closed)

Test results

In lieu of a CI, the latest test results on real hardware (Sipeed LicheePi4a) are:

hadrian/build -j --flavour=quick-validate --docs=none --config="config.timeout=12000" test

...

Unexpected results from:
TEST="T10052 T10508_api T17669 T18181 T20494 T5313 T7072 T8628 T8639_api dynCompileExpr ghcilink004 keep-cafs keep-cafs
-fail linker_unload linker_unload_multiple_objs linkwhole"

SUMMARY for test run started at Mon Jun 17 06:23:27 2024
1 day, 2:41:29.162070 spent to go through
   10022 total tests, which gave rise to
   45719 test cases, of which
   35670 were skipped
       7 had missing libraries

    9828 expected passes
     179 expected failures

       0 caused framework failures
       0 caused framework warnings
      16 unexpected passes
       0 unexpected failures
       0 unexpected stat failures
      26 fragile tests

Unexpected passes:
   /tmp/ghctest-b_7fvr1g/test   spaces/testsuite/tests/ghc-api/dynCompileExpr/dynCompileExpr.run
 dynCompileExpr [unexpected] (normal)
   /tmp/ghctest-b_7fvr1g/test   spaces/testsuite/tests/ghci/linking/ghcilink004.run
 ghcilink004 [unexpected] (normal)
   /tmp/ghctest-b_7fvr1g/test   spaces/testsuite/tests/rts/keep-cafs.run
 keep-cafs [unexpected] (normal)
   /tmp/ghctest-b_7fvr1g/test   spaces/testsuite/tests/rts/keep-cafs-fail.run
 keep-cafs-fail [unexpected] (normal)
   /tmp/ghctest-b_7fvr1g/test   spaces/testsuite/tests/rts/linker/linker_unload.run
 linker_unload [unexpected] (normal)
   /tmp/ghctest-b_7fvr1g/test   spaces/testsuite/tests/rts/linker/unload_multiple_objs/linker_unload_multiple_objs.run
 linker_unload_multiple_objs [unexpected] (normal)
   /tmp/ghctest-b_7fvr1g/test   spaces/testsuite/tests/driver/linkwhole/linkwhole.run
 linkwhole [unexpected] (normal)
   /tmp/ghctest-b_7fvr1g/test   spaces/testsuite/tests/ghc-api/T10052/T10052.run
 T10052 [unexpected] (normal)
   /tmp/ghctest-b_7fvr1g/test   spaces/testsuite/tests/ghc-api/T10508_api.run
 T10508_api [unexpected] (normal)
   /tmp/ghctest-b_7fvr1g/test   spaces/testsuite/tests/ghci/scripts/T17669.run
 T17669 [unexpected] (ghci)
   /tmp/ghctest-b_7fvr1g/test   spaces/testsuite/tests/ghc-api/T18181.run
 T18181 [unexpected] (normal)
   /tmp/ghctest-b_7fvr1g/test   spaces/testsuite/tests/rts/linker/T20494.run
 T20494 [unexpected] (normal)
   /tmp/ghctest-b_7fvr1g/test   spaces/testsuite/tests/driver/T5313.run
 T5313 [unexpected] (normal)
   /tmp/ghctest-b_7fvr1g/test   spaces/testsuite/tests/rts/linker/T7072.run
 T7072 [unexpected] (normal)
   /tmp/ghctest-b_7fvr1g/test   spaces/testsuite/tests/ghc-api/T8628.run
 T8628 [unexpected] (normal)
   /tmp/ghctest-b_7fvr1g/test   spaces/testsuite/tests/ghc-api/T8639_api.run
 T8639_api [unexpected] (normal)