[WinEH] Use operand bundles to describe call sites

SimplifyCFG allows tail merging with code which terminates in
unreachable which, in turn, makes it possible for an invoke to end up in
a funclet which it was not originally part of.

Using operand bundles on invokes allows us to determine whether or not
an invoke was part of a funclet in the source program.

Furthermore, it allows us to unambiguously answer questions about the
legality of inlining into call sites which the personality may have
trouble with.

Differential Revision: http://reviews.llvm.org/D15517

llvm-svn: 255674