Previous detection relied upon an arbitrary hard coded limit of 21
response files, which some code bases were running up against.
The new detection maintains a stack of processing response files and
explicitly checks if a newly encountered file is in the current stack.
Some bookkeeping data is necessary in order to detect when to pop the
stack.
Patch by Chris Glover.
Differential Revision: https://reviews.llvm.org/D62798
llvm-svn: 363005
5c99292520