Hotfix LLVM deprecation warning.

Author: mcourteaux

src/CodeGen_PTX_Dev.cpp

@@ -609,7 +609,7 @@ vector<char> CodeGen_PTX_Dev::compile_to_src() {
     // Allocate target machine
 
     std::string err_str;
-    const llvm::Target *llvm_target = TargetRegistry::lookupTarget(triple.str(), err_str);
+    const llvm::Target *llvm_target = TargetRegistry::lookupTarget(triple, err_str);
     internal_assert(llvm_target) << err_str << "\n";
 
     TargetOptions options;