Seems like there's an architecture error or something, the last line indicates you might have an error with the flag:

> zsh: illegal hardware instruction LLVM_SYMBOLIZER_PATH=/usr/local/opt/llvm/bin/llvm-symbolizer swift main.swift

that's not related to the symbolizer thing. It seems to just be part of the "index out of range" crash. I get the same thing without using the symbolizer.

    zsh: illegal hardware instruction  swift main.swift

Ouch, and yuk. I stand corrected!