rust-source: Fix remove_gcc_directory

The patch works for rust-native but not other recipes which change ${S}.
Set it to use the correct path so it works for llvm-rust, cargo and others,
maximising the space saving.

(From OE-Core rev: 1aee0bc109c1457159440c279ddc1fe5a8d89586)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-devtools/rust/rust-source.inc

@@ -17,7 +17,7 @@ RUSTSRC = "${WORKDIR}/rustc-${RUST_VERSION}-src"
 #After updating to Rust 1.85 we can revert this removal of "src/gcc"
 remove_gcc_directory() {
     # Ensure the gcc directory exists
-    gcc_dir="${S}/src/gcc"
+    gcc_dir="${RUSTSRC}/src/gcc"
     if [ -d "$gcc_dir" ]; then
         rm -rf "$gcc_dir"
     fi