swift-llvm-opt: adjust for SVN r276687

LLVM SVN r276687 ported the SymbolRewriter pass to the new PM.  This results in
the constructor being renamed.  Adjust the swift-llvm-opt tool accordingly.

Author: compnerd

tools/swift-llvm-opt/LLVMOpt.cpp

@@ -224,7 +224,7 @@ int main(int argc, char **argv) {
   // supported.
   initializeCodeGenPreparePass(Registry);
   initializeAtomicExpandPass(Registry);
-  initializeRewriteSymbolsPass(Registry);
+  initializeRewriteSymbolsLegacyPassPass(Registry);
   initializeWinEHPreparePass(Registry);
   initializeDwarfEHPreparePass(Registry);
   initializeSjLjEHPreparePass(Registry);