[Dominators] PR42041: Skip nullpointer successors
In Clang's CFG, we use nullpointers to represent unreachable nodes, for
example, in the included testfile, block B0 is unreachable from block
B1, resulting in a nullpointer dereference somewhere in
This patch fixes this issue by specializing
clang::CFG to not contain nullpointer successors.
Differential Revision: https://reviews.llvm.org/D62507