Update existing uses of /wd4267 to use the GN config

third_party/boringssl/BUILD.gn

Index: third_party/boringssl/BUILD.gn
diff --git a/third_party/boringssl/BUILD.gn b/third_party/boringssl/BUILD.gn
index d24586819e79f8c91067f8279d01b8e0af314e2e..9c75f1b8ed619cc6578c9210f653d6454b20f1bb 100644
--- a/third_party/boringssl/BUILD.gn
+++ b/third_party/boringssl/BUILD.gn
@@ -52,7 +52,12 @@ component("boringssl") {
   }
 
   configs -= [ "//build/config/compiler:chromium_code" ]
-  configs += [ "//build/config/compiler:no_chromium_code" ]
+  configs += [
+    "//build/config/compiler:no_chromium_code",
+    # TODO(davidben): Fix size_t truncations in BoringSSL.
+    # https://crbug.com/429039
+    "//build/config/compiler:no_size_t_to_int_warning",
+  ]
 
   # Also gets the include dirs from :openssl_config
   include_dirs = [
@@ -64,12 +69,6 @@ component("boringssl") {
     "src/crypto",
   ]
 
-  if (is_win) {
-    # TODO(davidben): Fix size_t truncations in BoringSSL.
-    # https://crbug.com/429039
-    cflags += [ "/wd4267" ]
-  }
-
   if (cpu_arch == "x64") {
     if (is_mac) {
       sources += gypi_values.boringssl_mac_x86_64_sources