Linux: Enable ODR violation detection.

build/common.gypi

 # Copyright (c) 2012 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 4389 matching lines @@
             'target_conditions': [
               ['_toolset=="target"', {
                 'ldflags': [
                   # Experimentation found that using four linking threads
                   # saved ~20% of link time.
                   # https://groups.google.com/a/chromium.org/group/chromium-dev/browse_thread/thread/281527606915bb36
                   # Only apply this to the target linker, since the host
                   # linker might not be gold, but isn't used much anyway.
                   '-Wl,--threads',
                   '-Wl,--thread-count=4',
+                  '-Wl,--detect-odr-violations',
                 ],
               }],
             ],
             'conditions': [
               ['release_valgrind_build==0 and order_profiling==0', {
                 'target_conditions': [
                   ['_toolset=="target"', {
                     'ldflags': [
                       '-Wl,--icf=safe',
                     ],
@@ skipping 1469 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }