MFC r252720:

Pull in r185594 from llvm trunk:

  Add MachineBasicBlock::addLiveIn().

  This function adds a live-in physical register to an MBB and ensures
  that it is copied to a virtual register immediately.

Pull in r185615 from llvm trunk:

  Live-in copies go *after* EH_LABELs.

  This will soon be tested by exception handling working at all.

Pull in r185617 from llvm trunk:

  Simplify landing pad lowering.

  Stop using the ISD::EXCEPTIONADDR and ISD::EHSELECTION when lowering
  landing pad arguments. These nodes were previously legalized into
  CopyFromReg nodes, but that never worked properly because the
  CopyFromReg node weren't guaranteed to be  scheduled at the top of the
  basic block.

  This meant the exception pointer and selector registers could be
  clobbered before being copied to a virtual register.

  This patch copies the two physical registers to virtual registers at
  the beginning of the basic block, and lowers the landingpad instruction
  directly to two CopyFromReg nodes reading the *virtual* registers. This
  is safe because virtual registers don't get clobbered.

  A future patch will remove the ISD::EXCEPTIONADDR and ISD::EHSELECTION
  nodes.

Together, these changes fix llvm PR 16038 ('qt4 webcore file results in
"Bad machine code: Using an undefined physical register"'), and should
make it possible again to compile the www/qt4-webkit port again on the
i386 arch, without using a CPUTYPE=i686 or higher setting.
MFC bsdconfig(8) and sysrc(8) from HEAD. (shazam!)