phosphor-snmp: use c++17

Update configure.ac to choose the c++17 standard

Change-Id: I7fe64e02441c06b7354fa9495e66c61328346012
Signed-off-by: Vernon Mauery <vernon.mauery@linux.intel.com>
diff --git a/configure.ac b/configure.ac
index f73d576..0cb8a84 100644
--- a/configure.ac
+++ b/configure.ac
@@ -17,6 +17,8 @@
 LT_PREREQ([2.4.6])
 LT_INIT([dlopen disable-static shared])
 
+AX_CXX_COMPILE_STDCXX_17([noext])
+
 # Checks for libraries.
 AX_PKG_CHECK_MODULES([SYSTEMD], [], [libsystemd >= 221], [],\
 [AC_MSG_ERROR(["Systemd version should be greater then 221."])])