linux-user: introduce preexit_cleanup

To avoid repeating ourselves move our preexit clean-up code into a
helper function. I figured the continuing effort to split of the
syscalls made it worthwhile creating a new file for it now.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>

linux-user/qemu.h

@@ -623,6 +623,14 @@ static inline int is_error(abi_long ret)
     return (abi_ulong)ret >= (abi_ulong)(-4096);
 }
 
+/**
+ * preexit_cleanup: housekeeping before the guest exits
+ *
+ * env: the CPU state
+ * code: the exit code
+ */
+void preexit_cleanup(CPUArchState *env, int code);
+
 /* Include target-specific struct and function definitions;
  * they may need access to the target-independent structures
  * above, so include them last.