Build as c++17

Change-Id: I5259037e9ea57b59e4cc7e9b5d7a46050f5f7c93
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/configure.ac b/configure.ac
index d565472..48c2a95 100644
--- a/configure.ac
+++ b/configure.ac
@@ -14,7 +14,7 @@
 AC_PROG_MAKE_SET
 
 # Checks for typedefs, structures, and compiler characteristics.
-AX_CXX_COMPILE_STDCXX_14([noext])
+AX_CXX_COMPILE_STDCXX_17([noext])
 AX_APPEND_COMPILE_FLAGS([-Wall -Werror], [CXXFLAGS])
 
 # Checks for libraries.