linux-user: Move thunk.c from top-level

So far, linux-user is the only user of these functions.
Clean up the build machinery by restricting it to linux-user.

Reviewed-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

MAINTAINERS

@@ -3077,7 +3077,6 @@ Usermode Emulation
 Overall usermode emulation
 M: Riku Voipio <riku.voipio@iki.fi>
 S: Maintained
-F: thunk.c
 F: accel/tcg/user-exec*.c
 F: include/user/
 F: common-user/

linux-user/meson.build

@@ -15,6 +15,7 @@ linux_user_ss.add(files(
   'signal.c',
   'strace.c',
   'syscall.c',
+  'thunk.c',
   'uaccess.c',
   'uname.c',
 ))

meson.build

@@ -2633,7 +2633,6 @@ subdir('linux-user')
 
 specific_ss.add_all(when: 'CONFIG_BSD_USER', if_true: bsd_user_ss)
 
-linux_user_ss.add(files('thunk.c'))
 specific_ss.add_all(when: 'CONFIG_LINUX_USER', if_true: linux_user_ss)
 
 common_user_ss = common_user_ss.apply(config_all, strict: false)