LTO: rename the various makeLTOModule overloads.

This rename makes it easier to identify the specific overload being called
in each particular case and makes future refactorings easier.

Differential Revision: http://reviews.llvm.org/D4370
gold plugin: move target initialization to the top of the onload function.

On at least my machine, ar does not register an all symbols read hook (which
previously triggered target initialization), but it does register a claim
files hook, which depends on the targets being initialized.

Differential Revision: http://reviews.llvm.org/D4372