Bring in a BumpPtrStringSaver from lld and simplify the interface.

StringSaver now always saves to a BumpPtrAllocator.

The only reason for having the virtual saveImpl is so lld can have a
thread safe version.

The reason for the distinct BumpPtrStringSaver class is to avoid the
virtual destructor.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239669 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Support/StringSaver.cpp

@@ -0,0 +1,19 @@
+//===-- StringSaver.cpp ---------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/StringSaver.h"
+
+using namespace llvm;
+
+const char *StringSaver::saveImpl(StringRef S) {
+  char *P = Alloc.Allocate<char>(S.size() + 1);
+  memcpy(P, S.data(), S.size());
+  P[S.size()] = '\0';
+  return P;
+}