fix: pass sccache variables to cross container with build.env.passthrough

Cross.toml

@@ -1,3 +1,15 @@
+[build.env]
+# CI uses an S3 endpoint to store sccache artifacts, so their config needs to
+# be available in the cross container as well
+passthrough = [
+    "RUSTC_WRAPPER",
+    "AWS_ACCESS_KEY_ID",
+    "AWS_SECRET_ACCESS_KEY",
+    "SCCACHE_BUCKET",
+    "SCCACHE_ENDPOINT",
+    "SCCACHE_S3_USE_SSL",
+]
+
 [target.aarch64-unknown-linux-musl]
 image = "rust-cross:aarch64-unknown-linux-musl"
 

cross/build.sh

@@ -22,9 +22,6 @@ $([[ $TARGET =~ arm ]] && echo 'ENV RUSTFLAGS="$RUSTFLAGS -Clink-arg=-lgcc -Clin
 # Strip symbols while compiling in release mode
 $([[ $@ =~ -r ]] && echo 'ENV RUSTFLAGS="$RUSTFLAGS -Clink-arg=-s"')
 
-# Support a rustc wrapper like sccache when cross-compiling
-ENV RUSTC_WRAPPER="$RUSTC_WRAPPER"
-
 # Make sure that rust-bindgen uses the correct include path when cross-compiling
 # See https://github.com/rust-lang/rust-bindgen#environment-variables for more information
 ENV BINDGEN_EXTRA_CLANG_ARGS="-I\$TARGET_PREFIX/include"