Bug 1245737 (part 0) - Fix a leak in DtoaState. r=sfink.

DtoaState has a field |p5s| that stores a linked list of Bigints which never
gets freed. This patch adds freeing code for it to destroydtoa().

This has never shown up before because DtoaState currently uses a private chunk
for allocations instead of malloc/free and that private chunk does get freed.
But the next patch will turn off the use of that private chunk so we now need
to free |p5s| so that ASAN doesn't complain.

The new code follows the bizarre local style used by dtoa.c.

js/src/dtoa.c

@@ -526,6 +526,14 @@ destroydtoa
 				FREE((void*)v);
 			}
 		}
+#ifdef Omit_Private_Memory
+	Bigint* p5 = GET_STATE(p5s);
+	while (p5) {
+		Bigint* tmp = p5;
+		p5 = p5->next;
+		FREE(tmp);
+		}
+#endif
 	FREE((void *)state);
 }