Add use_host_toolchain as a workflow_call arg (#1045)

Author: speednoisemovement

.github/workflows/build-toolchain.yml

@@ -138,6 +138,12 @@ on:
         default: false
         type: boolean
 
+      use_host_toolchain:
+        description: 'Use host toolchain (MSVC) instead of clang-cl/lld-link'
+        type: boolean
+        default: true
+        required: false
+
     secrets:
       SYMBOL_SERVER_PAT:
         required: true