Wrap CC and CXX with sccache by default

Build scripts that compile C/C++ (cc crate, libduckdb-sys's bundled
DuckDB, ring's assembly) are not cached by RUSTC_WRAPPER and dominate
warm CI time on Rust projects with heavy native deps. Export
CC=sccache cc and CXX=sccache c++ so those compilations land in the
same sccache backend as rustc.

Gated behind a new sccache-wrap-cc input (default "true") so callers
with build systems that do not tolerate multi-word CC/CXX can opt out.

Co-authored-by: Cursor <cursoragent@cursor.com>

.gitea/actions/rust-cache/action.yml

@@ -39,6 +39,10 @@ inputs:
     description: Optional S3 key prefix. Defaults to repository/runner/toolchain scope.
     default: ""
     required: false
+  sccache-wrap-cc:
+    description: Also wrap CC and CXX with sccache so build-script C/C++ compiles (e.g. libduckdb-sys, ring) hit the same cache as rustc. Set to "false" to opt out.
+    default: "true"
+    required: false
 
 outputs:
   sccache-enabled:
@@ -119,6 +123,10 @@ runs:
             echo "SCCACHE_S3_ENABLE_VIRTUAL_HOST_STYLE=true" >> "$GITHUB_ENV"
           fi
         fi
+        if [ '${{ inputs.sccache-wrap-cc }}' = 'true' ]; then
+          echo "CC=sccache cc" >> "$GITHUB_ENV"
+          echo "CXX=sccache c++" >> "$GITHUB_ENV"
+        fi
 
     - name: Start sccache
       if: ${{ inputs.sccache == 'true' }}