Remove several .c_str() to be forward-compatible with StringRef.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@90822 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Frontend/ASTUnit.cpp b/lib/Frontend/ASTUnit.cpp
index 8c2731b..8f66d4c 100644
--- a/lib/Frontend/ASTUnit.cpp
+++ b/lib/Frontend/ASTUnit.cpp
@@ -300,8 +300,8 @@
   Args.push_back("-fsyntax-only");
 
   llvm::sys::Path Path = llvm::sys::Path::GetMainExecutable(Argv0, MainAddr);
-  driver::Driver TheDriver(Path.getBasename().c_str(),Path.getDirname().c_str(),
-                           llvm::sys::getHostTriple().c_str(),
+  driver::Driver TheDriver(Path.getBasename(), Path.getDirname(),
+                           llvm::sys::getHostTriple(),
                            "a.out", false, Diags);
   llvm::OwningPtr<driver::Compilation> C(
     TheDriver.BuildCompilation(Args.size(), Args.data()));