Add support for switch and indirectbr edges. This works by densely numbering
all blocks which have such terminators, and then separately numbering the
possible successors. The predecessors write down a number, the successor knows
its own number (as a ConstantInt) and sends that and the pointer to the number
the predecessor wrote down to the runtime, who looks up the counter in a
per-function table.
Coverage data should now be functional, but I haven't tested it on anything
other than my 2-file synthetic test program for coverage.
llvm-svn: 130186
c58d293a6f