Use lld when building with mzcompose on macOS

Incremental compile time for bin/mzcompose improves from 6min28s to 13s on my system by using lld.

misc/python/materialize/xcompile.py

@@ -158,8 +158,13 @@ def cargo(
 
     if sys.platform == "darwin":
         _bootstrap_darwin(arch)
+        homebrew_prefix = spawn.capture(["brew", "--prefix"])
         sysroot = spawn.capture([f"{_target}-cc", "-print-sysroot"]).strip()
-        rustflags += [f"-L{sysroot}/lib"]
+        rustflags += [
+            f"-L{sysroot}/lib",
+            "-Clink-arg=-fuse-ld=lld",
+            f"-Clink-arg=-B{homebrew_prefix}/bin",
+        ]
         env.update(
             {
                 "CMAKE_SYSTEM_NAME": "Linux",
@@ -242,7 +247,7 @@ def _bootstrap_darwin(arch: Arch) -> None:
     # Building in Docker for Mac is painfully slow, so we install a
     # cross-compiling toolchain on the host and use that instead.
 
-    BOOTSTRAP_VERSION = "4"
+    BOOTSTRAP_VERSION = "5"
     BOOTSTRAP_FILE = MZ_ROOT / "target-xcompile" / target(arch) / ".xcompile-bootstrap"
     try:
         contents = BOOTSTRAP_FILE.read_text()
@@ -251,7 +256,7 @@ def _bootstrap_darwin(arch: Arch) -> None:
     if contents == BOOTSTRAP_VERSION:
         return
 
-    spawn.runv(["brew", "install", f"materializeinc/crosstools/{target(arch)}"])
+    spawn.runv(["brew", "install", "lld", f"materializeinc/crosstools/{target(arch)}"])
     spawn.runv(["rustup", "target", "add", target(arch)])
 
     BOOTSTRAP_FILE.parent.mkdir(parents=True, exist_ok=True)