Use lld to reduce macOS release binary size

.bazelrc

@@ -317,6 +317,18 @@ build:release_macos --config=release_unix
 # data in releases.
 build:release_macos --linkopt="-Wl,-no_data_in_code_info"
 build:release_macos --linkopt="-Wl,-no_function_starts"
+# Enable lld identical code folding to significantly reduce binary size.
+build:release_macos --config=macos_lld_icf
+
+# On macOS, compile using LLD (19 or higher is compatible with the default flags added by
+# apple_support). Requires Homebrew's lld package to be installed. This is less CPU intensive than
+# the system linker, but also slightly slower in terms of wall time since it is less parallel. More
+# importantly, it allows us to enable LLD's ICF pass, which significantly decreases binary sizes.
+# We also want to enable ICF for Linux, but there it causes warnings when dynamically linking with
+# libc++.
+build:macos_lld --linkopt="-fuse-ld=/opt/homebrew/bin/ld64.lld"
+build:macos_lld_icf --config=macos_lld
+build:macos_lld_icf --linkopt="-Wl,--icf=safe"
 
 build:release_windows --config=release
 # Windows uses /O2 as its preferred optimization setting and enabled by bazel in the opt

.github/workflows/release.yml

@@ -96,6 +96,8 @@ jobs:
         if: runner.os == 'macOS'
         run: |
           sudo xcode-select -s "/Applications/Xcode_15.1.app"
+          # Install lld
+          brew install lld
       - name: Setup Windows
         if: runner.os == 'Windows'
         run: |