Use -std=c++14 for GN bootstrap

See https://chromium.googlesource.com/chromium/src/+/5a9b923e371351d2ca64b47b9cac5f39d4fb7e86
(https://chromium-review.googlesource.com/583635) where chromium switched
to C++14.

Without this change, bootstrap fails.

Bug: none
Change-Id: I393ff80f9b0f504d1623f48e37c74802aaed12d3
Reviewed-on: https://chromium-review.googlesource.com/623671
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Brett Wilson <brettw@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#496245}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 85bd0394c6825a810421698f0f9578de636761aa
diff --git a/tools/gn/bootstrap/bootstrap.py b/tools/gn/bootstrap/bootstrap.py
index 41e4ae3..004d81c 100755
--- a/tools/gn/bootstrap/bootstrap.py
+++ b/tools/gn/bootstrap/bootstrap.py
@@ -348,7 +348,7 @@
         '-pipe',
         '-fno-exceptions'
     ])
-    cflags_cc.extend(['-std=c++11', '-Wno-c++11-narrowing'])
+    cflags_cc.extend(['-std=c++14', '-Wno-c++11-narrowing'])
     if is_aix:
      cflags.extend(['-maix64'])
      ldflags.extend([ '-maix64 -Wl,-bbigtoc' ])