meson: Replace softmmu_ss -> system_ss

We use the user_ss[] array to hold the user emulation sources,
and the softmmu_ss[] array to hold the system emulation ones.
Hold the latter in the 'system_ss[]' array for parity with user
emulation.

Mechanical change doing:

  $ sed -i -e s/softmmu_ss/system_ss/g $(git grep -l softmmu_ss)

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230613133347.82210-10-philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

target/sh4/meson.build

@@ -7,8 +7,8 @@ sh4_ss.add(files(
   'translate.c',
 ))
 
-sh4_softmmu_ss = ss.source_set()
-sh4_softmmu_ss.add(files('monitor.c'))
+sh4_system_ss = ss.source_set()
+sh4_system_ss.add(files('monitor.c'))
 
 target_arch += {'sh4': sh4_ss}
-target_softmmu_arch += {'sh4': sh4_softmmu_ss}
+target_softmmu_arch += {'sh4': sh4_system_ss}