[analyzer] Fix infinite recursion in printing macros

In the commited testfile, macro expansion (the one implemented for the plist
output) runs into an infinite recursion. The issue originates from the algorithm
being faulty, as in

#define value REC_MACRO_FUNC(value)

the "value" is being (or at least attempted) expanded from the same macro.

The solved this issue by gathering already visited macros in a set, which does
resolve the crash, but will result in an incorrect macro expansion, that would
preferably be fixed down the line.

Patch by Tibor Brunner!

Differential Revision: https://reviews.llvm.org/D57891

llvm-svn: 355705