* Added lowering hook for external weak global address. It inserts a load

* Added lowering hook for external weak global address. It inserts a load
  for Darwin.
* Added lowering hook for ISD::RET. It inserts CopyToRegs for the return
  value (or store / fld / copy to ST(0) for floating point value). This
  eliminate the need to write C++ code to handle RET with variable number
  of operands.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@24888 91177308-0d34-0410-b5e6-96231b3b80d8