I have built Crystal compiler using binaries of LLVM8 provided by the LLVM team, and it works fine without upgrading ld for CentOS 6 and Fedora 22, currently.
To use officially distributed Crystal compiler under CentOS 6, Fedora 22, or Ubuntu trusty, you may use conda to upgrade ld. See BFD version 2.20.51.0.2-5.47.el6_9.1 20100205 internal error, aborting at reloc.c line 443 in bfd_get_reloc_size · Issue #8323 · crystal-lang/crystal · GitHub. I did not test this, so I don’t know how long take to upgrade ld.
You can use Ubuntu xenial (or even more recent), which includes newer ld.
Oh, I tested under the CentOS 6 using official Crystal compiler and bdwgc provided by CentOS team, it causes same problem. Sorry.