build: Remove build system support for gold plugin, except under ChromeOS.

build/config/compiler/BUILD.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/android/config.gni")
 import("//build/config/chrome_build.gni")
 import("//build/config/chromecast_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/toolchain/cc_wrapper.gni")
 import("//build/toolchain/toolchain.gni")
@@ skipping 452 matching lines @@
 
   # Add flags for link-time optimization. These flags enable
   # optimizations/transformations that require whole-program visibility at link
   # time, so they need to be applied to all translation units, and we may end up
   # with miscompiles if only part of the program is compiled with LTO flags. For
   # that reason, we cannot allow targets to enable or disable these flags, for
   # example by disabling the optimize configuration.
   # 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" ]
 
       # 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.
-      if (use_lld) {
-        ldflags += [
-          "-Wl,--thinlto-jobs=8",
-          "-Wl,--thinlto-cache-dir=" +
-              rebase_path("$root_out_dir/thinlto-cache", root_build_dir),
-        ]
-      } else {
-        ldflags += [ "-Wl,-plugin-opt,jobs=8" ]
-      }
+      ldflags += [
+        "-Wl,--thinlto-jobs=8",
+        "-Wl,--thinlto-cache-dir=" +
+            rebase_path("$root_out_dir/thinlto-cache", root_build_dir),
+      ]
     } else {
       cflags += [ "-flto" ]
       ldflags += [ "-flto" ]
 
       # Apply a lower LTO optimization level as the default is too slow.
       if (is_linux) {
-        if (use_lld) {
-          ldflags += [ "-Wl,--lto-O1" ]
-        } else {
-          ldflags += [ "-Wl,-plugin-opt,O1" ]
-        }
+        ldflags += [ "-Wl,--lto-O1" ]
       } else if (is_mac) {
         ldflags += [ "-Wl,-mllvm,-O1" ]
       }
     }
 
     cflags += [ "-fwhole-program-vtables" ]
     ldflags += [ "-fwhole-program-vtables" ]
 
     # Work-around for http://openradar.appspot.com/20356002
     if (is_mac) {
       ldflags += [ "-Wl,-all_load" ]
     }
 
     # Allows the linker to apply --gc-sections and ICF to the LTO object file.
     # Also, when targeting ARM, without this flag, LTO produces a .text section
     # that is larger than the maximum call displacement, preventing the linker
     # from relocating calls (http://llvm.org/PR22999).
     if (is_linux) {
-      if (use_lld) {
-        ldflags += [
-          "-Wl,-mllvm,-function-sections",
-          "-Wl,-mllvm,-data-sections",
-        ]
-      } else {
-        ldflags += [
-          "-Wl,-plugin-opt,-function-sections",
-          "-Wl,-plugin-opt,-data-sections",
-        ]
-      }
+      ldflags += [
+        "-Wl,-mllvm,-function-sections",
+        "-Wl,-mllvm,-data-sections",
+      ]
     }
   }
 
   # Pass the same C/C++ flags to the objective C/C++ compiler.
   cflags_objc += cflags_c
   cflags_objcc += cflags_cc
 
   # Assign any flags set for the C compiler to asmflags so that they are sent
   # to the assembler. The Windows assembler takes different types of flags
   # so only do so for posix platforms.
@@ skipping 1208 matching lines @@
 
 if (is_ios || is_mac) {
   # On Mac and iOS, this enables support for ARC (automatic ref-counting).
   # See http://clang.llvm.org/docs/AutomaticReferenceCounting.html.
   config("enable_arc") {
     common_flags = [ "-fobjc-arc" ]
     cflags_objc = common_flags
     cflags_objcc = common_flags
   }
 }