Roll AFL 2.31b:2.38b and switch coverage to use trace-pc-guard.

third_party/afl/src/libdislocator/libdislocator.so.c

Index: third_party/afl/src/libdislocator/libdislocator.so.c
diff --git a/third_party/afl/src/libdislocator/libdislocator.so.c b/third_party/afl/src/libdislocator/libdislocator.so.c
index 1d4648f3ce8ad8b258c7f46e4c8c1413e69347b5..0dfc98e6058a4ab0cb8f5507a82ec05537c598f8 100644
--- a/third_party/afl/src/libdislocator/libdislocator.so.c
+++ b/third_party/afl/src/libdislocator/libdislocator.so.c
@@ -64,7 +64,7 @@
 /* Canary & clobber bytes: */
 
 #define ALLOC_CANARY  0xAACCAACC
-#define ALLOC_CLOBBER 0x41
+#define ALLOC_CLOBBER 0xCC
 
 #define PTR_C(_p) (((u32*)(_p))[-1])
 #define PTR_L(_p) (((u32*)(_p))[-2])
@@ -89,7 +89,8 @@ static void* __dislocator_alloc(size_t len) {
 
   void* ret;
 
-  if (total_mem + len > max_mem) {
+
+  if (total_mem + len > max_mem || total_mem + len < total_mem) {
 
     if (hard_fail)
       FATAL("total allocs exceed %u MB", max_mem / 1024 / 1024);