[analyzer] Do not cache out on some shared implicit AST nodes

Some AST nodes which stands for implicit initialization is shared. The analyzer
will do the same evaluation on the same nodes resulting in the same state. The
analyzer will "cache out", i.e. it thinks that it visited an already existing
node in the exploded graph. This is not true in this case and we lose coverage.
Since these nodes do not really require any processing from the analyzer
we just omit them from the CFG.

Differential Revision: https://reviews.llvm.org/D71371