[LLVM-3.9] Specify that we are using the legacy interface

LLVM pass manager infrastructure is currently getting rewritten to be
more flexible, but the rewrite isn't complete yet.

src/rustllvm/PassWrapper.cpp

@@ -267,7 +267,7 @@ LLVMRustAddLibraryInfo(LLVMPassManagerRef PMB,
 // similar code in clang's BackendUtil.cpp file.
 extern "C" void
 LLVMRustRunFunctionPassManager(LLVMPassManagerRef PM, LLVMModuleRef M) {
-    FunctionPassManager *P = unwrap<FunctionPassManager>(PM);
+    llvm::legacy::FunctionPassManager *P = unwrap<llvm::legacy::FunctionPassManager>(PM);
     P->doInitialization();
     for (Module::iterator I = unwrap(M)->begin(),
          E = unwrap(M)->end(); I != E; ++I)
@@ -294,7 +294,7 @@ LLVMRustWriteOutputFile(LLVMTargetMachineRef Target,
                         LLVMModuleRef M,
                         const char *path,
                         TargetMachine::CodeGenFileType FileType) {
-  PassManager *PM = unwrap<PassManager>(PMR);
+  llvm::legacy::PassManager *PM = unwrap<llvm::legacy::PassManager>(PMR);
 
   std::string ErrorInfo;
   std::error_code EC;
@@ -320,7 +320,7 @@ extern "C" void
 LLVMRustPrintModule(LLVMPassManagerRef PMR,
                     LLVMModuleRef M,
                     const char* path) {
-  PassManager *PM = unwrap<PassManager>(PMR);
+  llvm::legacy::PassManager *PM = unwrap<llvm::legacy::PassManager>(PMR);
   std::string ErrorInfo;
 
   std::error_code EC;