[WinEH] Make setjmp work correctly with EH

32-bit X86 EH on Windows utilizes a stack of registration nodes
allocated and deallocated on entry/exit.  A registration node contains a
bunch of EH personality specific information like which try-state we are
currently in.

Because a setjmp target allows control flow from arbitrary program
points, there is no way to ensure that the try-state we are in is
correctly updated once we transfer control.

MSVC compatible compilers, like MSVC and ICC, utilize runtime helpers to
reinitialize the try-state when a longjmp occurs.  This is implemented
by adding additional arguments to _setjmp3: the desired try-state and
a helper routine to update the try-state.

Differential Revision: http://reviews.llvm.org/D17721

llvm-svn: 262241