[llvm-symbolizer] Support debug file lookup using build ID

Build ID is a protocol for looking up debug files that's already
supported by various tools including debuggers. For example, when
locating debug files, gdb would check the following directories:

- /usr/lib/debug/.build-id/ab/cdef1234.debug
- /usr/bin/ls.debug
- /usr/bin/.debug/ls.debug
- /usr/lib/debug/usr/bin/ls.debug

llvm-symbolizer currently consults all of these except for build ID
based one. This patch implements support for build ID lookup. The
set of debug directories to search is specified by the new option:
--debug-file-directory, whose name matches the debug-file-directory
variable used by gdb for the same purpose.

Differential Revision: https://reviews.llvm.org/D70759