configure: Poison all current target-specific #defines

We are generating a lot of target-specific defines in the *-config-devices.h
and *-config-target.h files. Using them in common code is wrong and leads
to very subtle bugs since a "#ifdef CONFIG_SOMETHING" is not working there
as expected. To avoid these issues, we are already poisoning many of the
macros in include/exec/poison.h - but it's cumbersome to maintain this
list manually. Thus let's generate an additional list of poisoned macros
automatically from the current config switches - this should give us a
much better test coverage via the different CI configurations.

Note that CONFIG_TCG (which is also defined in config-host.h) and
CONFIG_USER_ONLY are special, so we have to filter these out.

Message-Id: <20210414112004.943383-5-thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

include/exec/poison.h

@@ -4,6 +4,8 @@
 #ifndef HW_POISON_H
 #define HW_POISON_H
 
+#include "config-poison.h"
+
 #pragma GCC poison TARGET_I386
 #pragma GCC poison TARGET_X86_64
 #pragma GCC poison TARGET_AARCH64