stubs: Restrict fw_cfg to system emulation

fw_cfg_arch_key_name() stub is only required for sysemu.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Message-Id: <20220111184309.28637-2-f4bug@amsat.org>

stubs/meson.build

@@ -11,7 +11,6 @@ stub_ss.add(files('icount.c'))
 stub_ss.add(files('dump.c'))
 stub_ss.add(files('error-printf.c'))
 stub_ss.add(files('fdset.c'))
-stub_ss.add(files('fw_cfg.c'))
 stub_ss.add(files('gdbstub.c'))
 stub_ss.add(files('get-vm-name.c'))
 if linux_io_uring.found()
@@ -51,6 +50,7 @@ if have_block
   stub_ss.add(files('replay-tools.c'))
 endif
 if have_system
+  stub_ss.add(files('fw_cfg.c'))
   stub_ss.add(files('semihost.c'))
   stub_ss.add(files('usb-dev-stub.c'))
   stub_ss.add(files('xen-hw-stub.c'))