github: use faster linkers in CI

This shaves off something like 20 to 40 seconds for Linux. It’s
seemingly within the margin of error for Windows, so not sure if
we’ll want to keep it there.

.cargo/config-ci.toml

@@ -2,8 +2,15 @@
 debug = "none"
 incremental = false
 
+[target.x86_64-unknown-linux-gnu]
+rustflags = ["-Clink-arg=-fuse-ld=mold"]
+
+[target.aarch64-unknown-linux-gnu]
+rustflags = ["-Clink-arg=-fuse-ld=mold"]
+
+[target.x86_64-pc-windows-msvc]
+linker = "rust-lld.exe"
 # NOTE: on Windows, build with the static CRT, so that produced .exe files don't
 # depend on vcruntime140.dll; otherwise the user requires visual studio if they
 # download a raw .exe
-[target.x86_64-pc-windows-msvc]
 rustflags = ["-Ctarget-feature=+crt-static"]

.github/workflows/ci.yml

@@ -80,6 +80,10 @@ jobs:
     - uses: taiki-e/install-action@0f58b6a196e0d71c72fd459ab8fd8b228f85f669
       with:
         tool: nextest,taplo-cli
+    - name: Install mold
+      uses: rui314/setup-mold@f80524ca6eeaa76759b57fb78ddce5d87a20c720
+      with:
+        make-default: false
     - name: Build
       run: >-
         cargo build