[Bug preprocessor/69093] New: implement -fmacro-backtrace-limit

["patrick.pelissier at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69093

            Bug ID: 69093
           Summary: implement -fmacro-backtrace-limit
           Product: gcc
           Version: 5.3.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: preprocessor
          Assignee: unassigned at gcc dot gnu.org
          Reporter: patrick.pelissier at gmail dot com
  Target Milestone: ---

Recent gcc performs full backtrace when error / warning appear within a macro
but has not any option to limit its size.

This makes gcc hard to use for debugging deferred recursive macros (See
https://github.com/pfultz2/Cloak/wiki/C-Preprocessor-tricks,-tips,-and-idioms):
in such cases, the backtrace is huge (more than 5000 lines of backtrace per
instance) and useless.

clang has the option -fmacro-backtrace-limit for this purpose.