win32: convert exit codes

Add two utility functions to convert Windows process exit codes.

- exit_code_to_wait_status() converts to a POSIX wait status.
  This is used in ash and the implementations of system(3) and
  mingw_wait3().

- exit_code_to_posix() converts to a POSIX exit code.  (Not that
  POSIX has much to say about them.)

As a result it's possible for more applets to report when child
processes are killed as if by a signal.  'time', 'drop' and 'su -W',
for example.

Adds 64-80 bytes.

1 files changed, 1 insertions, 6 deletions

diff --git a/win32/system.c b/win32/system.c
index 00b594242..c718d9948 100644
--- a/win32/system.c
+++ b/win32/system.c
@@ -6,7 +6,6 @@ int mingw_system(const char *cmd)
         intptr_t proc;
         HANDLE h;
         DWORD ret = 0;
-        int sig;
 
         if (cmd == NULL)
                 return 1;
@@ -19,9 +18,5 @@ int mingw_system(const char *cmd)
         GetExitCodeProcess(h, &ret);
         CloseHandle(h);
 
-        // Was process terminated as if by a signal?
-        sig = ret >> 24;
-        if (sig != 0 && ret == sig << 24 && is_valid_signal(sig))
-                return sig;
-        return ret << 8;
+        return exit_code_to_wait_status(ret);
 }