MFH: r407167

During the exp-run in bug 206074, it was found that emulators/simh gives
errors with a recent clang 3.8.0 snapshot [1]:

/usr/bin/ld: unrecognized option '-plugin'

And more of such linking errors. This is because the simh main Makefile
attempts to use -flto -fwhole-program with clang, but this support
depends on the correctly link time optimization infrastructure being
installed (e.g. the LLVMgold.so plugin, and more).

Since LTO is not available yet in base, here is a patch to disable the
use of these options more thorougly.

Approved by: ports-secteam (delphij)
PR: 206411