[PM] Use a simpler technique to drop optional analysis manager arguments

when invoking run methods.

This technique was suggested by Dinesh Dwivedi who also wrote the
original patch. During the code review, they explained to me that this
isn't a fully general technique as we need to know the signatures of the
method candidates. Since this is really a narrower utility, I switched
the names and structure to be more clearly a specialized run method
invoke helper and commented it accordingly. I still think this is
a pretty big win.

Very sorry to Dinesh for the extreme delay in landing this patch. I've
been far to busy poking at other things.

Original review: http://reviews.llvm.org/D3543

llvm-svn: 238305