[FileSystem] Remove Exists() from FileSpec

This patch removes the Exists method from FileSpec and updates its uses
with calls to the FileSystem.

Differential revision: https://reviews.llvm.org/D53845

llvm-svn: 345854
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
index 2a2448c..1a852fc 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
@@ -1640,7 +1640,7 @@
     dwo_file.AppendPathComponent(dwo_name);
   }
 
-  if (!dwo_file.Exists())
+  if (!FileSystem::Instance().Exists(dwo_file))
     return nullptr;
 
   const lldb::offset_t file_offset = 0;
@@ -3879,7 +3879,7 @@
     module_spec.GetSymbolFileSpec() =
         FileSpec(m_obj_file->GetFileSpec().GetPath() + ".dwp", false);
     FileSpec dwp_filespec = Symbols::LocateExecutableSymbolFile(module_spec);
-    if (dwp_filespec.Exists()) {
+    if (FileSystem::Instance().Exists(dwp_filespec)) {
       m_dwp_symfile = SymbolFileDWARFDwp::Create(GetObjectFile()->GetModule(),
                                                  dwp_filespec);
     }