[lldb] Minidump: check for .text hash match with directory

When opening a minidump, we might discover that it reports a UUID for a
module that doesn't match the build ID, but rather a hash of the .text
section (according to either of two different hash functions, used by
breakpad and Facebook respectively).  The current logic searches for a
module by filename only to check the hash; this change updates it to
first search by directory+filename.  This is important when the
directory specified in the minidump must be interpreted relative to a
user-provided sysoort, as the leaf directory won't be in the search path
in that case.

Also add a regression test; without this change, module validation fails
because we have just the placeholder module which reports as its path
the platform path in the minidump.

Reviewed By: clayborg

Differential Revision: https://reviews.llvm.org/D89155

(cherry picked from commit d30797b4)