build: compile with --gnu++17

Enables C++17 features.

Author: richardlau

common.gypi

@@ -382,7 +382,7 @@
       }],
       [ 'OS in "linux freebsd openbsd solaris android aix cloudabi"', {
         'cflags': [ '-Wall', '-Wextra', '-Wno-unused-parameter', ],
-        'cflags_cc': [ '-fno-rtti', '-fno-exceptions', '-std=gnu++14' ],
+        'cflags_cc': [ '-fno-rtti', '-fno-exceptions', '-std=gnu++17' ],
         'defines': [ '__STDC_FORMAT_MACROS' ],
         'ldflags': [ '-rdynamic' ],
         'target_conditions': [
@@ -526,7 +526,7 @@
           ['clang==1', {
             'xcode_settings': {
               'GCC_VERSION': 'com.apple.compilers.llvm.clang.1_0',
-              'CLANG_CXX_LANGUAGE_STANDARD': 'gnu++14',  # -std=gnu++14
+              'CLANG_CXX_LANGUAGE_STANDARD': 'gnu++17',  # -std=gnu++17
               'CLANG_CXX_LIBRARY': 'libc++',
             },
           }],