Build as c++17

Change-Id: Ia6cfb3915174db1c55f1dd7adedd40c69000a217
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/configure.ac b/configure.ac
index 277a361..875b3f6 100644
--- a/configure.ac
+++ b/configure.ac
@@ -13,7 +13,7 @@
 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([-fpic -Wall -Werror], [CXXFLAGS])
 
 # Checks for libraries.