Merge bitcoin/bitcoin#33626: ci: run native fuzz with MSAN job

1e6e32fa8a ci: run native fuzz with MSAN job (fanquake)
3784d15bcd ci: use LLVM libcxx 21.1.5 (fanquake)

Pull request description:

  I think this job should exist in this repo (not just qa-assets), if the alternative is double-handling changes to the interpreter. #32998 made changes which were then re-changed in #33600, to work around a false positive.

  The unchached runtime of this job with `-lg` is `~32m`, with `-md` it's `~43m`.

  Timeout is set to 150m, as the slow GHA runners were close to hitting a 120m limit.

ACKs for top commit:
  maflcko:
    lgtm ACK 1e6e32fa8a
  dergoegge:
    utACK 1e6e32fa8a

Tree-SHA512: afd4cb0039f4f49ddc23f5553a5bf6d5ceffbc12d91acd6890d5cc40c30b7421b23d04f305983d94c862daa6fc07535b1331d7fa2a8ebfe9f19c20d83d95c692

.github/workflows/ci.yml

@@ -533,6 +533,12 @@ jobs:
             timeout-minutes: 120
             file-env: './ci/test/00_setup_env_native_tsan.sh'
 
+          - name: 'MSan, fuzz'
+            cirrus-runner: 'ghcr.io/cirruslabs/ubuntu-runner-amd64:24.04-md'
+            fallback-runner: 'ubuntu-24.04'
+            timeout-minutes: 150
+            file-env: './ci/test/00_setup_env_native_fuzz_with_msan.sh'
+
           - name: 'MSan, depends'
             cirrus-runner: 'ghcr.io/cirruslabs/ubuntu-runner-amd64:24.04-lg'
             fallback-runner: 'ubuntu-24.04'
@@ -561,7 +567,7 @@ jobs:
         run: sed -i "s|\${INSTALL_BCC_TRACING_TOOLS}|true|g" ./ci/test/00_setup_env_native_asan.sh
 
       - name: Set mmap_rnd_bits
-        if: ${{ env.CONTAINER_NAME == 'ci_native_tsan' || env.CONTAINER_NAME == 'ci_native_msan' }}
+        if: ${{ env.CONTAINER_NAME == 'ci_native_tsan' || env.CONTAINER_NAME == 'ci_native_msan' || env.CONTAINER_NAME == 'ci_native_fuzz_msan' }}
         # Prevents crashes due to high ASLR entropy
         run: sudo sysctl -w vm.mmap_rnd_bits=28