ash: fix use of pid/handle in waitpid_child

Previously spawn was returning a process handle which was treated as a
pid in certain circumstances.  This resulted in the following failing:

   find . -type f | sed xargs -n 1 sed -n '1 p'

It should output the first line of each file but stopped after the
first.

1 files changed, 1 insertions, 0 deletions

diff --git a/include/mingw.h b/include/mingw.h
index bfdf2cccd..efb17e137 100644
--- a/include/mingw.h
+++ b/include/mingw.h
@@ -450,6 +450,7 @@ DIR *mingw_opendir(const char *path);
 #define PRIuMAX "I64u"
 
 pid_t FAST_FUNC mingw_spawn(char **argv);
+intptr_t FAST_FUNC mingw_spawn_proc(char **argv);
 int mingw_execv(const char *cmd, const char *const *argv);
 int mingw_execvp(const char *cmd, const char *const *argv);
 int mingw_execve(const char *cmd, const char *const *argv, const char *const *envp);