CodeGen: make the type match the comment for a libcall

Fix the type for a (runtime) library call to match both the comment and
the runtime implementation.  As it happens, the type being used matched,
this just makes it more precise.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@305638 91177308-0d34-0410-b5e6-96231b3b80d8