Reapply "[NFC] Explicitly pass a VFS when creating DiagnosticsEngine (llvm#115852)"

This reverts commit a1153cd with fixes
to lldb breakages.

Fixes llvm#117145.

Author: kadircet

lldb/source/Commands/CommandObjectTarget.cpp

@@ -2200,7 +2200,7 @@ class CommandObjectTargetModulesDumpClangPCMInfo : public CommandObjectParsed {
     }
 
     clang::CompilerInstance compiler;
-    compiler.createDiagnostics(*llvm::vfs::getRealFileSystem());
+    compiler.createDiagnostics(*FileSystem::Instance().GetVirtualFileSystem());
 
     const char *clang_args[] = {"clang", pcm_path};
     compiler.setInvocation(clang::createInvocation(clang_args));

lldb/source/Plugins/ExpressionParser/Clang/ClangModulesDeclVendor.cpp

@@ -706,8 +706,9 @@ ClangModulesDeclVendor::Create(Target &target) {
   auto diag_options_up =
       clang::CreateAndPopulateDiagOpts(compiler_invocation_argument_cstrs);
   llvm::IntrusiveRefCntPtr<clang::DiagnosticsEngine> diagnostics_engine =
-      clang::CompilerInstance::createDiagnostics(diag_options_up.release(),
-                                                 new StoringDiagnosticConsumer);
+      clang::CompilerInstance::createDiagnostics(
+          *FileSystem::Instance().GetVirtualFileSystem(),
+          diag_options_up.release(), new StoringDiagnosticConsumer);
 
   Log *log = GetLog(LLDBLog::Expressions);
   LLDB_LOG(log, "ClangModulesDeclVendor's compiler flags {0:$[ ]}",