RuntimeDyld cleanup:

RuntimeDyld cleanup:

- Improved parameter names for clarity
- Added comments
- emitCommonSymbols should return void because its return value is not being
  used anywhere
- Attempt to reduce the usage of the RelocationValueRef type. Restricts it
  for a single goal and may serve as a step for eventual removal.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@155908 91177308-0d34-0410-b5e6-96231b3b80d8