Make is_win_fastlink imply -fstandalone-debug for clang

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 1542 matching lines @@
     cflags = [ "/Zi" ]  # Produce PDB file, no edit and continue.
 
     if (is_win_fastlink) {
       # Tell VS 2015+ to create a PDB that references debug
       # information in .obj and .lib files instead of copying
       # it all. This flag is incompatible with /PROFILE
       ldflags = [ "/DEBUG:FASTLINK" ]
     } else {
       ldflags = [ "/DEBUG" ]
     }
+
+    if (is_clang) {
+      # /DEBUG:FASTLINK requires every object file to have standalone debug
+      # information.
+      if (is_win_fastlink) {
+        cflags += [ "-fstandalone-debug" ]
+      } else {
+        cflags += [ "-fno-standalone-debug" ]
+      }
+    }
   } else {
     if (is_mac || is_ios) {
       cflags = [ "-gdwarf-2" ]
       if (is_mac && enable_dsyms) {
         # If generating dSYMs, specify -fno-standalone-debug. This was
         # originally specified for https://crbug.com/479841 because dsymutil
         # could not handle a 4GB dSYM file. But dsymutil from Xcodes prior to
         # version 7 also produces debug data that is incompatible with Breakpad
         # dump_syms, so this is still required (https://crbug.com/622406).
         cflags += [ "-fno-standalone-debug" ]
@@ skipping 66 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
   }
 }