Late last year r191835 removed a largely unmaintained legacy PGO
infrastructure, but some of the docs were missed. Since these docs are
for things that don't actually exist anymore, they should be removed.
llvm-svn: 210165
Some references to llvm-gcc were so crusty that I wasn't sure how to
proceed and so I've left them intact.
I also slipped in a quick peephole fix to use a :doc: link instead of
raw HTML link.
llvm-svn: 201619
