Fix kexidb build with -std=c++20.

This solves issue #70.

Signed-off-by: François Andriot <francois.andriot@thalesgroup.com>

kexi/kexidb/drivers/configure.in.in

@@ -307,7 +307,7 @@ if test "$compile_pgsql_plugin" = "yes"; then
     )
     if test "x$pqxx_exceptions" = "xno"; then
       AC_MSG_RESULT(no)
-      for CXX_STD_TEST in 11 14 17; do
+      for CXX_STD_TEST in 11 14 17 20; do
         AC_MSG_CHECKING([PostgreSQL build with C++$CXX_STD_TEST])
         CXXFLAGS="$SAVED_CXXFLAGS $PQXX_CXXFLAGS -std=c++$CXX_STD_TEST"
         AC_TRY_COMPILE([