travis: See if OSX generates crash dumps

I know for a fact we've had sccache segfault on various platforms and we've also
historically had a lot of problems with the linker on OSX. Let's just poke
around in the crash log directory to see if anything exists. If in the future we
see a build we think segfaulted *and* there's contents here then we can add some
bits that actually print out the logs.

.travis.yml

@@ -153,9 +153,17 @@ after_failure:
       echo "#### Build failed; Disk usage after running script:";
       df -h;
       du . | sort -nr | head -n100
+
+  # One of these is the linux sccache log, one is the OSX sccache log. Instead
+  # of worrying about what system we are just cat both. One of these commands
+  # will fail but that's ok, they'll both get executed.
   - cat obj/tmp/sccache.log
   - cat /tmp/sccache.log
 
+  # Random attempt at debugging currently. Just poking around in here to see if
+  # anything shows up.
+  - ls $HOME/Library/Logs/DiagnosticReports/
+
 # Save tagged docker images we created and load them if they're available
 before_cache:
   - docker history -q rust-ci |