Test was failing (could not execute: pgmlc) for arm (which uses
the llvm backend) due to the `-pgmlc pgmlc` in OPTIONS_GHC. It
was also failing on amd64 in the same way when `-fllvm` was
added to the command line. Its safe to remove because the
compiler should already know which llvm tool to use.

Test Plan: validate

Reviewers: dterei, austin

Subscribers: bgamari, thomie

Differential Revision: https://phabricator.haskell.org/D874