build: enable C++20

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Ic4081b95dada39918fa2d65f7b2031e117e76cd9
diff --git a/configure.ac b/configure.ac
index 2faca39..81b100c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -29,7 +29,7 @@
     AC_MSG_ERROR(["Requires sdbus++"]))
 
 # Checks for typedefs, structures, and compiler characteristics.
-AX_CXX_COMPILE_STDCXX_17([noext])
+AX_CXX_COMPILE_STDCXX([20],[noext])
 AX_APPEND_COMPILE_FLAGS([-fpic -Wall -Werror], [CXXFLAGS])
 
 # Checks for library functions.