Bug 1690937 - Build cbindgen with a sysroot. r=firefox-build-system-reviewers,sheehan,mhentges

Similarly to sccache, we need to use clang.

Differential Revision: https://phabricator.services.mozilla.com/D104134

taskcluster/ci/toolchain/cbindgen.yml

@@ -23,12 +23,15 @@ linux64-cbindgen:
     treeherder:
         symbol: TL(cbindgen)
     worker:
+        docker-image: {in-tree: deb10-toolchain-build}
         max-run-time: 1800
     run:
         arguments: ['x86_64-unknown-linux-gnu']
     fetches:
         toolchain:
+            - linux64-clang-11
             - linux64-rust-1.47
+            - linux64-sysroot
 
 macosx64-cbindgen:
     treeherder:

taskcluster/scripts/misc/build-cbindgen.sh

@@ -29,6 +29,10 @@ if [ "$TARGET" == "x86_64-apple-darwin" ]; then
   export PATH="$MOZ_FETCHES_DIR/llvm-dsymutil/bin:$PATH"
   export PATH="$MOZ_FETCHES_DIR/cctools/bin:$PATH"
   export RUSTFLAGS="-C linker=$GECKO_PATH/taskcluster/scripts/misc/osx-cross-linker"
+elif [ "$TARGET" == "x86_64-unknown-linux-gnu" ]; then
+  export CC="$MOZ_FETCHES_DIR/clang/bin/clang"
+  export CFLAGS_x86_64_unknown_linux_gnu="--sysroot=$MOZ_FETCHES_DIR/sysroot"
+  export RUSTFLAGS="-C linker=$CC -C link-arg=--sysroot=$MOZ_FETCHES_DIR/sysroot"
 fi
 
 export PATH="$(cd $MOZ_FETCHES_DIR && pwd)/rustc/bin:$PATH"