Added cp-graviton building of llvm

.github/workflows/create_llvm.yml

@@ -6,15 +6,26 @@ on:
       - main
     paths:
       - '.github/workflows/create_llvm.yml'
+  pull_request:
+    paths:
+      - '.github/workflows/create_llvm.yml'         
   workflow_dispatch:
 
 jobs:
   create_llvm_cache:
     strategy:
       matrix:
         version: [17, 18]
-        os: [ubuntu-22.04]
+        os: [ubuntu-22.04, cp-graviton]
         build_type: [Release, RelAssert]
+        exclude:
+          # Temporary to test just graviton
+          - os: ubuntu-22.04
+          - os: cp-graviton
+            version: 17
+          - os: cp-graviton
+            build_type: Release
+            version: 18
         include:
           # We want to set flags related to particular matrix dimensions. To do this
           # we need to create default values first, and then against particular matrix