Breakpad: Match the new UUID algorithm in minidumps

D59433 and D60501 changed the way UUIDs are computed from minidump
files. This was done to synchronize the U(G)UID representation with the
native tools of given platforms, but it created a mismatch between
minidumps and breakpad files.

This updates the breakpad algorithm to match the one found in minidumps,
and also adds a couple of tests which should fail if these two ever get
out of sync. Incidentally, this means that the module id in the breakpad
files is almost identical to our notion of UUIDs, so the computation
algorithm can be somewhat simplified.

llvm-svn: 358500