Eliminate DefaultImageName from the Driver constructor

All callers were passing in "a.out" or garbage so a sensible default works fine
here as a cleanup.

This also brings about the possibility of adapting the value based on the
driver's compatibility mode in future.

The setting can still be changed via Driver::DefaultImageName as needed.

llvm-svn: 208926
diff --git a/clang/lib/Tooling/Tooling.cpp b/clang/lib/Tooling/Tooling.cpp
index 5f4c46d..610bfc8 100644
--- a/clang/lib/Tooling/Tooling.cpp
+++ b/clang/lib/Tooling/Tooling.cpp
@@ -54,10 +54,8 @@
 /// \brief Builds a clang driver initialized for running clang tools.
 static clang::driver::Driver *newDriver(clang::DiagnosticsEngine *Diagnostics,
                                         const char *BinaryName) {
-  const char *DefaultOutputName = "a.out";
   clang::driver::Driver *CompilerDriver = new clang::driver::Driver(
-    BinaryName, llvm::sys::getDefaultTargetTriple(),
-    DefaultOutputName, *Diagnostics);
+      BinaryName, llvm::sys::getDefaultTargetTriple(), *Diagnostics);
   CompilerDriver->setTitle("clang_based_tool");
   return CompilerDriver;
 }