Use a separate config.h for config like defines.

This allows an easier way to share config parameters between unit tests
and the bionic code.

It also fixes a problem where the 32 bit bionic tests based on glibc, or
the cts list executable did not have the pvalloc,valloc tests.

Change-Id: Ib47942cb8a278252faa7498a6ef23e9578db544f

tests/malloc_test.cpp

@@ -22,9 +22,7 @@
 #include <malloc.h>
 #include <unistd.h>
 
-#if defined(__BIONIC__)
-#include <libc/bionic/malloc_debug_common.h>
-#endif
+#include "private/bionic_config.h"
 
 TEST(malloc, malloc_std) {
   // Simple malloc test.