Turn some C-style vararg into variadic templates

Module::getOrInsertFunction is using C-style vararg instead of
variadic templates.

From a user prospective, it forces the use of an annoying nullptr
to mark the end of the vararg, and there's not type checking on the
arguments. The variadic template is an obvious solution to both
issues.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@299925 91177308-0d34-0410-b5e6-96231b3b80d8
24 files changed