Merge bitcoin/bitcoin#31425: CI: Add Riscv bare metal job

b36730a3ef  Add CI job for riscv bare metal (TheCharlatan)
bfdbf513f6 Add CI job for producing a static bare metal binary (TheCharlatan)
a9a1d92a1d build: Add option for building for bare metal envs (TheCharlatan)

Pull request description:

  This adds a CI job for building the static consensus library and linking it to an executable. It uses newlib-cygwin as a C library for the final linking step. This ensure compatibility with this target going forward and can serve as a starting point for enabling bare metal builds for the entire kernel library. This would have also caught the error fixed in #31365.

ACKs for top commit:
  fanquake:
    ACK b36730a3ef
  willcl-ark:
    reACK b36730a3ef

Tree-SHA512: c199260f243e20df7f6a537e6c1eaf3d32e23f8fc78b9a8e2b75d9feff3830ef61279e93093dacdceb99e8eb010321b4c1c644e2ad9e266f0ca1ae736baa20ae

.github/workflows/ci.yml

@@ -529,6 +529,12 @@ jobs:
             timeout-minutes: 120
             file-env: './ci/test/00_setup_env_native_msan.sh'
 
+          - name: 'riscv32 bare metal, static libbitcoin_consensus'
+            warp-runner: 'warp-ubuntu-latest-x64-16x'
+            fallback-runner: 'ubuntu-latest'
+            timeout-minutes: 120
+            file-env: './ci/test/00_setup_env_riscv_bare_cross.sh'
+
     steps:
       - *ANNOTATION_PR_NUMBER