replay: do not build if TCG is not available

this fixes non-TCG builds broken recently by replay reverse debugging.

Stub the needed functions in stub/, splitting roughly between functions
needed only by system emulation, by system emulation and tools,
and by everyone.  This includes duplicating some code in replay/, and
puts the logic for non-replay related events in the replay/ module (+
the stubs), so this should be revisited in the future.

Surprisingly, only _one_ qtest was affected by this, ide-test.c, which
resulted in a buzz as the bh events were never delivered, and the bh
never executed.

Many other subsystems _should_ have been affected.

This fixes the immediate issue, however a better way to group replay
functionality to TCG-only code could be developed in the long term.

Signed-off-by: Claudio Fontana <cfontana@suse.de>
Message-Id: <20201013192123.22632-4-cfontana@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/net/meson.build b/net/meson.build
index 1c7e3a3..1076b0a 100644
--- a/net/meson.build
+++ b/net/meson.build
@@ -7,7 +7,6 @@
   'eth.c',
   'filter-buffer.c',
   'filter-mirror.c',
-  'filter-replay.c',
   'filter-rewriter.c',
   'filter.c',
   'hub.c',
@@ -17,6 +16,8 @@
   'util.c',
 ))
 
+softmmu_ss.add(when: 'CONFIG_TCG', if_true: files('filter-replay.c'))
+
 softmmu_ss.add(when: 'CONFIG_L2TPV3', if_true: files('l2tpv3.c'))
 softmmu_ss.add(when: slirp, if_true: files('slirp.c'))
 softmmu_ss.add(when: ['CONFIG_VDE', vde], if_true: files('vde.c'))