build: enable C++20

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I2c00b2af93ba231253ecf129a1bd3ea51ddbdcb1
diff --git a/configure.ac b/configure.ac
index 1f33112..4946730 100644
--- a/configure.ac
+++ b/configure.ac
@@ -26,7 +26,7 @@
 PKG_CHECK_MODULES([PHOSPHOR_LOGGING], [phosphor-logging])
 
 # 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 header files.