Disable Warning 4702 for the PGO builds.

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")
 if (cpu_arch == "arm") {
   import("//build/config/arm.gni")
 }
 if (is_posix) {
   import("//build/config/gcc/gcc_version.gni")
@@ skipping 749 matching lines @@
 # On Windows, turns up the optimization level. This implies whole program
 # optimization and link-time code generation which is very expensive and should
 # be used sparingly. For non-Windows, this is the same as "optimize".
 config("optimize_max") {
   cflags = common_optimize_on_cflags
   ldflags = common_optimize_on_ldflags
   if (is_win) {
     cflags += [
       "/Ot",   # Favor speed over size.
       "/GL",   # Whole program optimization.
+      # Disable Warning 4702 ("Unreachable code") for the WPO/PGO builds.
+      # Probably anything that this would catch that wouldn't be caught in a
+      # normal build isn't going to actually be a bug, so the incremental value
+      # of C4702 for PGO builds is likely very small.
+      "/wd4702",
     ]
   } else {
     cflags += [
       "-O2",
     ]
   }
 }
 
 # Symbols ----------------------------------------------------------------------
 
@@ skipping 13 matching lines @@
   } else {
     cflags = [ "-g1" ]
   }
 }
 
 config("no_symbols") {
   if (!is_win) {
     cflags = [ "-g0" ]
   }
 }