[FileSpec] Delegate common operations to llvm::sys::path

With the recent changes in FileSpec to use LLVM's path style, it is
possible to delegate a bunch of common path operations to LLVM's path
helpers. This means we only have to maintain a single implementation and
at the same time can benefit from the efforts made by the rest of the
LLVM community.

This is part one of a set of patches. There was no obvious way to split
this so I just worked from top to bottom.

Differential revision: https://reviews.llvm.org/D48084

llvm-svn: 334615
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
index b7dd461..203c22e 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
@@ -1653,7 +1653,7 @@
             // (corresponding to .dwo) so we simply skip it.
             if (m_obj_file->GetFileSpec()
                         .GetFileNameExtension()
-                        .GetStringRef() == "dwo" &&
+                        .GetStringRef() == ".dwo" &&
                 llvm::StringRef(m_obj_file->GetFileSpec().GetPath())
                     .endswith(dwo_module_spec.GetFileSpec().GetPath())) {
               continue;