Always enable -Wsuggest-override

configure.ac

@@ -447,10 +447,7 @@ if test "$CXXFLAGS_overridden" = "no"; then
   AX_CHECK_COMPILE_FLAG([-Wduplicated-cond], [WARN_CXXFLAGS="$WARN_CXXFLAGS -Wduplicated-cond"], [], [$CXXFLAG_WERROR])
   AX_CHECK_COMPILE_FLAG([-Wlogical-op], [WARN_CXXFLAGS="$WARN_CXXFLAGS -Wlogical-op"], [], [$CXXFLAG_WERROR])
   AX_CHECK_COMPILE_FLAG([-Woverloaded-virtual], [WARN_CXXFLAGS="$WARN_CXXFLAGS -Woverloaded-virtual"], [], [$CXXFLAG_WERROR])
-  dnl -Wsuggest-override is broken with GCC before 9.2
+  AX_CHECK_COMPILE_FLAG([-Wsuggest-override], [WARN_CXXFLAGS="$WARN_CXXFLAGS -Wsuggest-override"], [], [$CXXFLAG_WERROR])
-  dnl https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78010
-  AX_CHECK_COMPILE_FLAG([-Wsuggest-override], [WARN_CXXFLAGS="$WARN_CXXFLAGS -Wsuggest-override"], [], [$CXXFLAG_WERROR],
-                        [AC_LANG_SOURCE([[struct A { virtual void f(); }; struct B : A { void f() final; };]])])
   AX_CHECK_COMPILE_FLAG([-Wunreachable-code-loop-increment], [WARN_CXXFLAGS="$WARN_CXXFLAGS -Wunreachable-code-loop-increment"], [], [$CXXFLAG_WERROR])
   AX_CHECK_COMPILE_FLAG([-Wimplicit-fallthrough], [WARN_CXXFLAGS="$WARN_CXXFLAGS -Wimplicit-fallthrough"], [], [$CXXFLAG_WERROR])