build: Prepare for building clang without ENABLE_LINKER_BUILD_ID=ON

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 9137028913079075f8c41a1e43753d231662ff34..ab8a7dab416d3ae02e056618cc19ad59197bb148 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -277,6 +277,16 @@ config("compiler") {
       }
     }
 
+    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) {