build: Prepare for building clang without ENABLE_LINKER_BUILD_ID=ON

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/compiler/compiler.gni")
 import("//build/config/nacl/config.gni")
 import("//build/toolchain/cc_wrapper.gni")
 import("//build/toolchain/toolchain.gni")
@@ skipping 259 matching lines @@
 
         if (enable_full_stack_frames_for_profiling) {
           cflags += [
             "-fno-inline",
             "-fno-optimize-sibling-calls",
           ]
         }
       }
     }
 
+    if (is_official_build) {
+      # Explicitly pass --build-id to ld. Compilers used to always pass this
+      # implicitly but don't any more (in particular clang when built without
+      # ENABLE_LINKER_BUILD_ID=ON). The crash infrastructure does need a build
+      # id, so explicitly enable it in official builds. It's not needed in
+      # unofficial builds and computing it does slow down the link, so go with
+      # faster links in unofficial builds.
+      ldflags += [ "-Wl,--build-id=sha1" ]

[Roland McGrath, 2017/03/07 18:16:13]

Gold supports --build-id=tree, which is much faster.

[Nico, 2017/03/07 18:37:45]

lld supports that too, but apparently just maps it to sha1 :-D

Does tree produce the same number? Do you know if crash relies on getting sha1s?

I'm trying to not change behavior for official binaries for now, and just make
non-official links faster for now.

+    }
+
     defines += [ "_FILE_OFFSET_BITS=64" ]
 
     if (!is_android) {
       defines += [
         "_LARGEFILE_SOURCE",
         "_LARGEFILE64_SOURCE",
       ]
     }
 
     if (!is_nacl) {
@@ skipping 1416 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
   }
 }