clang/linux: Build with -g0 if fastbuild=1 is set (e.g. on the buildbots)

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index eb7b37098d1c3034d3d9c9e8e42a2e29481ce93d..645c337a3c1f4b6f31544e8e6aeb6f580eeb4491 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -549,6 +549,14 @@
               'debug_extra_cflags': '-g1',
             },
           }],
+          # Clang creates chubby debug information, which makes linking very
+          # slow. For now, don't create debug information with clang.  See
+          # http://crbug.com/70000
+          ['OS=="linux" and clang==1', {
+            'variables': {
+              'debug_extra_cflags': '-g0',
+            },
+          }],
         ],  # conditions for fastbuild.
       }],  # fastbuild!=0
       ['selinux==1', {