[llvm-symbolizer] Introduce the -dsym-hint option.

llvm-symbolizer will consult one of the .dSYM paths passed via -dsym-hint
if it fails to find the .dSYM bundle at the default location.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220004 91177308-0d34-0410-b5e6-96231b3b80d8