CRASH relocating ArchLinux glibc 2.25

I'm filing this based on an email thread on the users list: https://groups.google.com/forum/#!topic/dynamorio-users/4B2Jf34we4U

Some key snippets:

> ...client crashes during relocation.
> ArchLinux, glibc 2.25, Linux 4.11.3 64-bit
> I traced it to this specific case https://github.com/DynamoRIO/dynamorio/blob/17106ec7faeeb170d53f4ceea6a69bc447455deb/core/unix/module_elf.c#L1776 (ELF_R_IRELATIVE) in module_elf.c. The first time it's hit, it looks like the loader crashes.
> ...commenting out the aforementioned case statement seems to work fine for an empty test client.
> It looks like it hits that case 8 times when loading libc 2.25 on my system (details above).
> ...
> This was ArchLinux specific. A new glibc released today (still v2.25) fixes this issue.
>