Add builder to try

Author: tmandry

.github/workflows/ci.yml

@@ -586,6 +586,9 @@ jobs:
             env:
               CODEGEN_BACKENDS: "llvm,cranelift"
             os: ubuntu-20.04-16core-64gb
+          - name: x86_64-gnu-experimental
+            os: ubuntu-20.04-16core-64gb
+            env: {}
     timeout-minutes: 600
     runs-on: "${{ matrix.os }}"
     steps:

src/ci/github-actions/ci.yml

@@ -737,6 +737,9 @@ jobs:
             env:
               CODEGEN_BACKENDS: llvm,cranelift
             <<: *job-linux-16c
+          - name: x86_64-gnu-experimental
+            <<: *job-linux-16c
+
 
   master:
     name: master