Restore stdint.h for android-3..19 to the original headers

$NDK/tests/standalone/run.sh fail to run with last update on stdint.h
to android-20 level.  Restore stdint.h for fear of the new one breaking
the existing apps

Also fix signal_portable.h to use SIGRTMIN/MAX in old headers
(which got renamed to __SIGRTMIN in new header)

Also change _JBLEN to 1024 which shall be large enough to store CPU
states for forseable future.

Change-Id: Ia9c03558a258c10434eb8e6985adc122532feaa3

ndk/sources/android/libportable/common/include/asm/signal_portable.h

@@ -103,6 +103,14 @@ typedef unsigned long sigset_portable_t;
  *    lib-portable application can interact with. MIPS has
  *    an additional 63 signals.
  */
+
+#ifndef __SIGRTMIN
+#define __SIGRTMIN SIGRTMIN
+#endif
+#ifndef __SIGRTMAX
+#define __SIGRTMAX SIGRTMAX
+#endif
+
 #define SIGRT_1 (__SIGRTMIN + 1)
 #define SIGRT_2 (__SIGRTMIN + 2)
 #define SIGRT_3 (__SIGRTMIN + 3)