ndk: Fix wait4() declarations

wait4() was incorrectly declared in <sys/wait.h>, but only added to the
C library in Android 4.3 (API level 18) [1]

This patch:

- Removes the wait4() declarations for any <sys/wait.h> header before
  API level 19.

- Brings the API level 19 <sys/wait.h> which correctly declares wait4().

- Update the libc.so.functions.txt for API level 19 of all platforms
  to include the exported symbol.

NOTE: This does not bring the static libc.a to API level 19, which means
      it is stuck at API level 9 for ARM.

See [2] for the corresponding NDK tests.

http://b.android.com/19854

[1] 17a8b0db63
[2] https://android-review.googlesource.com/#/c/72000/

Change-Id: I7735473d177c44f43b09bb6738e9914945cd4d0a

ndk/platforms/android-3/include/sys/wait.h

@@ -47,7 +47,6 @@ __BEGIN_DECLS
 extern pid_t  wait(int *);
 extern pid_t  waitpid(pid_t, int *, int);
 extern pid_t  wait3(int *, int, struct rusage *);
-extern pid_t  wait4(pid_t, int *, int, struct rusage *);
 
 __END_DECLS