Use lld linker when building rustc.

This was unintentionally removed in
https://chromium-review.googlesource.com/c/chromium/src/+/4100425
when removing adjacent flags in the same string.

We use lld linker for all C++ linking in the chromium build too, and
we pass the same flag to Rust for linux and mac as well.

[email protected], [email protected]

Bug: 1401042
Change-Id: Icbf8ddf100ab525e5ff03144f4a6b1e21bf6feb5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4220699
Reviewed-by: Hans Wennborg <[email protected]>
Auto-Submit: danakj <[email protected]>
Commit-Queue: Hans Wennborg <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1101504}
NOKEYCHECK=True
GitOrigin-RevId: 0faa2994034a93d10a81bf6763fbe03205925505

Author: danakj

build_rust.py

@@ -255,6 +255,8 @@ def RunXPy(sub, args, llvm_bins_path, zlib_path, libxml2_dirs, build_mac_arm,
         RUSTENV['AR'] = os.path.join(llvm_bins_path, 'llvm-ar')
         RUSTENV['CC'] = os.path.join(llvm_bins_path, 'clang')
         RUSTENV['CXX'] = os.path.join(llvm_bins_path, 'clang++')
+        RUSTENV['RUSTFLAGS_BOOTSTRAP'] += f' -Clink-arg=-fuse-ld=lld'
+        RUSTENV['RUSTFLAGS_NOT_BOOTSTRAP'] += f' -Clink-arg=-fuse-ld=lld'
 
     if sys.platform == 'darwin':
         # The system/xcode compiler would find system SDK correctly, but