Revert "Add --program-prefix support to build"

Revert "Add --program-prefix support to build"

The Apple buildbots are set up to pass --target to configure for both
cross- and non-cross-compile builds, and the standard autoconf response
to this is to set the program prefix to '<target>-'. Until we can figure
out the proper way to handle this (don't pass --target? pass an explicit
--program-prefix=""? don't auto-populate program_prefix with target_alias?)
it's more important to keep the buildbots running.

This reverts r164633 / ba48ceb1a3802e20e781ef04ea2573ffae2ac414.

llvm-svn: 164651