Don't expose all BSD extensions.

Just expose the ones that bionic historically leaked.

Also, many of the M_* constants in <math.h> are actually POSIX.

Change-Id: I6275df84c5866b872b71f1c8ed14e2aada12b793
diff --git a/libc/include/limits.h b/libc/include/limits.h
index 84effa7..cb86aec 100644
--- a/libc/include/limits.h
+++ b/libc/include/limits.h
@@ -66,7 +66,7 @@
 #define ULONG_LONG_MAX  ULLONG_MAX
 #endif
 
-#if defined(__USE_BSD)
+#if defined(__USE_BSD) || defined(__BIONIC__) /* Historically bionic exposed these. */
 #if defined(__LP64__)
 #define SIZE_T_MAX ULONG_MAX
 #else