We don't pass classes with a copy-constructor or destructor byval, so the...

We don't pass classes with a copy-constructor or destructor byval, so the address takes up an integer register (if one is available).  Make sure the x86-64 ABI implementation takes that into account properly.

The fixed implementation is compatible with the implementation both gcc and llvm-gcc use.

rdar://9686430 . (This is the issue that was reported in the thread "[LLVMdev] Segfault calling LLVM libs from a clang-compiled executable".)

llvm-svn: 134059