[Bug sanitizer/59136] [4.9 Regression] llvm-symbolizer shouldn't be started always

[samsonov at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59136

--- Comment #6 from Alexey Samsonov <samsonov at google dot com> ---
(In reply to Richard Biener from comment #5)
> No processes should be launched at all.  Blocks the release - please make it
> at least configurable to be able to turn it off.

External process will only be launched if a user has llvm-symbolizer binary in
his PATH. This behaivor can also be turned off with a runtime option
(ASAN_OPTIONS=symbolize=false).