add configuration for self-init

This needs to be disabled for compatibility with the exploit protection
compatibility mode on GrapheneOS. hardened_malloc shouldn't be trying to
initialize itself when exploit protection compatibility mode is enabled.
This has to be handled in our Bionic integration instead.

h_malloc.c

@@ -1183,11 +1183,13 @@ static inline unsigned init(void) {
     return arena;
 }
 
+#if CONFIG_SELF_INIT
 // trigger early initialization to set up pthread_atfork and protect state as soon as possible
 COLD __attribute__((constructor(101))) static void trigger_early_init(void) {
     // avoid calling init directly to skip it if this isn't the malloc implementation
     h_free(h_malloc(16));
 }
+#endif
 
 // Returns 0 on overflow.
 static size_t get_large_size_class(size_t size) {