Revert of build: Remove build system support for gold plugin.

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 11b7190462a7a35c3872d21a22b6935349733bc2..7f57d912d6f1ec60650af9ce04dc3bf61fc37683 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -470,8 +470,6 @@
   # TODO(pcc): Make this conditional on is_official_build rather than on gn
   # flags for specific features.
   if (!is_debug && (allow_posix_link_time_opt || is_cfi) && !is_nacl) {
-    assert(use_lld, "POSIX LTO requires LLD")
-
     if (use_thin_lto) {
       cflags += [ "-flto=thin" ]
       ldflags += [ "-flto=thin" ]
@@ -479,11 +477,15 @@
       # Limit the parallelism to avoid too agressive competition between
       # linker jobs. This is still suboptimal to a potential dynamic
       # resource allocation scheme, but should be good enough.
-      ldflags += [
-        "-Wl,--thinlto-jobs=8",
-        "-Wl,--thinlto-cache-dir=" +
-            rebase_path("$root_out_dir/thinlto-cache", root_build_dir),
-      ]
+      if (use_lld) {
+        ldflags += [
+          "-Wl,--thinlto-jobs=8",
+          "-Wl,--thinlto-cache-dir=" +
+              rebase_path("$root_out_dir/thinlto-cache", root_build_dir),
+        ]
+      } else {
+        ldflags += [ "-Wl,-plugin-opt,jobs=8" ]
+      }
     } else {
       # Note: ThinLTO does not currently have this feature implemented
       # For Full LTO, it provides a measurable runtime speedup of Chrome.
@@ -498,7 +500,11 @@
 
       # Apply a lower LTO optimization level as the default is too slow.
       if (is_linux) {
-        ldflags += [ "-Wl,--lto-O1" ]
+        if (use_lld) {
+          ldflags += [ "-Wl,--lto-O1" ]
+        } else {
+          ldflags += [ "-Wl,-plugin-opt,O1" ]
+        }
       } else if (is_mac) {
         ldflags += [ "-Wl,-mllvm,-O1" ]
       }
@@ -514,10 +520,17 @@
     # that is larger than the maximum call displacement, preventing the linker
     # from relocating calls (http://llvm.org/PR22999).
     if (is_linux) {
-      ldflags += [
-        "-Wl,-mllvm,-function-sections",
-        "-Wl,-mllvm,-data-sections",
-      ]
+      if (use_lld) {
+        ldflags += [
+          "-Wl,-mllvm,-function-sections",
+          "-Wl,-mllvm,-data-sections",
+        ]
+      } else {
+        ldflags += [
+          "-Wl,-plugin-opt,-function-sections",
+          "-Wl,-plugin-opt,-data-sections",
+        ]
+      }
     }
   }