target/sh4: Build 'gdbstub.c' once for system binaries

'gdbstub.c' can now be built once for all qemu-system-sh4*
binaries.

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20260219191955.83815-41-philmd@linaro.org>

target/sh4/meson.build

@@ -1,7 +1,6 @@
 sh4_ss = ss.source_set()
 sh4_ss.add(files(
   'cpu.c',
-  'gdbstub.c',
   'helper.c',
   'op_helper.c',
   'translate.c',
@@ -9,8 +8,13 @@ sh4_ss.add(files(
 
 sh4_common_system_ss = ss.source_set()
 sh4_common_system_ss.add(files(
+  'gdbstub.c',
   'monitor.c',
 ))
 
+sh4_user_ss = ss.source_set()
+sh4_user_ss.add(files('gdbstub.c'))
+
 target_arch += {'sh4': sh4_ss}
+target_user_arch += {'sh4': sh4_user_ss}
 target_common_system_arch += {'sh4': sh4_common_system_ss}