As part of the cleanup when a process dies, tell watchpoints to forget their...

As part of the cleanup when a process dies, tell watchpoints to forget their previously recorded values

Because types are not reliably protected against the death of their owners, having ValueObjects lurking around like that past the useful lifetime of their owner processes is a potential source of crashes
That is - in itself - worth fixing at some point, but for this case, watchpoints holding on to old values don't offer enough value to make the larger fix worth

Fixes rdar://19788756

llvm-svn: 228777