mimo-updater: use -std=gnu++14 for C++ compilation

libchrome after r780000 uprev uses C++14 (-std=gnu++14).

BUG=chromium:1094927
TEST=emerge-fizz mimo-updater

Change-Id: Id631892d2d564c1c0232d04465999a495c759cea
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/mimo-updater/+/2409398
Commit-Queue: Qijiang Fan <fqj@google.com>
Tested-by: Grace Cham <hscham@chromium.org>
Reviewed-by: Qijiang Fan <fqj@google.com>
Reviewed-by: Joe Tessler <jrt@chromium.org>
diff --git a/common.mk b/common.mk
index 320a132..9e64539 100644
--- a/common.mk
+++ b/common.mk
@@ -318,7 +318,7 @@
 COMMON_CFLAGS-gcc := -fvisibility=internal -ggdb3 -Wa,--noexecstack
 COMMON_CFLAGS-clang := -fvisibility=hidden -ggdb
 COMMON_CFLAGS := -Wall -Werror -fno-strict-aliasing $(SSP_CFLAGS) -O1 -Wformat=2
-CXXFLAGS += $(COMMON_CFLAGS) $(COMMON_CFLAGS-$(CXXDRIVER)) -std=gnu++11
+CXXFLAGS += $(COMMON_CFLAGS) $(COMMON_CFLAGS-$(CXXDRIVER)) -std=gnu++14
 CFLAGS += $(COMMON_CFLAGS) $(COMMON_CFLAGS-$(CDRIVER)) -std=gnu11
 CPPFLAGS += -D_FORTIFY_SOURCE=2