Add symbolizer for ASan as well.  Make binary a PIE.
Use FD_SETSIZE rather than manually doing the accounting on the maximum number of FDs.  Mark shovecars as skipping MSan checks, it appears that FD_ISSET is not MSan-clean.  Use C++ strings for the command buffer.  It seems that the unordered_map was not matching the C-style strings correctly in every case.