Enable ThinLTO cache.

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index 1f8968670781cf0c6a810bffa6bb47170c0d8979..74e3f19f2d12279de99b045cb5e7c3d8daedafaa 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -471,7 +471,11 @@ config("compiler") {
       # linker jobs. This is still suboptimal to a potential dynamic
       # resource allocation scheme, but should be good enough.
       if (use_lld) {
-        ldflags += [ "-Wl,--thinlto-jobs=8" ]
+        ldflags += [
+          "-Wl,--thinlto-jobs=8",
+          "-Wl,--thinlto-cache-dir=" +
+              rebase_path("$root_out_dir/thinlto-cache", root_build_dir),
+        ]
       } else {
         ldflags += [ "-Wl,-plugin-opt,jobs=8" ]
       }