Provide better callstack for Dr. Fuzz with -fuzz_replace_buffer

Option -fuzz_replace_buffer allows Dr.Fuzz allocate application memory to replace input buffer for flexible input mutation.
Current callstack for the malloc from Dr. Fuzz is something like:

```
~~Dr.M~~ Error #1: WARNING: heap allocation failed
~~Dr.M~~ # 0 repeatme
~~Dr.M~~ # 1 main
```

On Windows, it is even worse:

```
~~Dr.M~~ # 0 repeatme
~~Dr.M~~ # 1 __tmainCRTStartup [f:\dd\vctools\crt_bld\self_x86\crt\src\crt0.c:278]
~~Dr.M~~ # 2 KERNEL32.dll!BaseThreadInitThunk
```

The `main` function frame is skipped probably due to the frame pointer is pointing to the previous frame.
It would be helpful to provide a better callstack.