Follow-up to r219534 to make symbolization more robust.

1) Explicitly provide important arguments to llvm-symbolizer,
not relying on defaults.
2) Be more defensive about symbolizer output.

This might fix weird failures on ninja-x64-msvc-RA-centos6 buildbot.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219541 91177308-0d34-0410-b5e6-96231b3b80d8