Attempt to fix TestMiniDump on windows

It was failing because the modules names were coming out as
C:\Windows\System32/MSVCP120D.dll (last separator is a forward slash) on
windows.

There are two issues at play here:
- the first problem is that the paths in minidump were being parsed as a
  host path. This meant that on posix systems the whole path was
  interpreted as a file name.
- on windows the path was split into a directory-filename pair
  correctly, but then when it was reconsituted, the last separator ended
  up being a forward slash because SBFileSpec.fullpath was joining them
  with '/' unconditionally.

I fix the first issue by parsing the minidump paths according to the
path syntax of the host which produced the dump, which should make the
test behavior on posix&windows identical. The last path will still be a
forward slash because of the second issue. We should probably fix the
"fullpath" property to do something smarter in the future.

llvm-svn: 330314