Define PTHREAD_KEYS_MAX and _POSIX_THREAD_KEYS_MAX in a POSIX-compliant way.

Also make sysconf use PTHREAD_STACK_MIN rather than redefining its
own, different, constant.

Bug: 9997352
Change-Id: I9a8e7d2b18e691439abfb45533e82c36eee9e81d
diff --git a/libc/include/sys/limits.h b/libc/include/sys/limits.h
index 2d0d11e..f1080fe 100644
--- a/libc/include/sys/limits.h
+++ b/libc/include/sys/limits.h
@@ -176,9 +176,9 @@
 #define  _POSIX_JOB_CONTROL         1    /* job control is a Linux feature */
 
 #define _POSIX_THREAD_DESTRUCTOR_ITERATIONS 4 /* the minimum mandated by POSIX */
-#define PTHREAD_DESTRUCTOR_ITERATIONS 4
+#define PTHREAD_DESTRUCTOR_ITERATIONS _POSIX_THREAD_DESTRUCTOR_ITERATIONS
 #define _POSIX_THREAD_KEYS_MAX 128            /* the minimum mandated by POSIX */
-/* TODO: our PTHREAD_KEYS_MAX is currently too low to be posix compliant! */
+#define PTHREAD_KEYS_MAX _POSIX_THREAD_KEYS_MAX
 #define _POSIX_THREAD_THREADS_MAX 64          /* the minimum mandated by POSIX */
 #define PTHREAD_THREADS_MAX                   /* bionic has no specific limit */