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/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index 44c41b6..67ead61 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -47,12 +47,11 @@
 
 Driver::Driver(StringRef ClangExecutable,
                StringRef DefaultTargetTriple,
-               StringRef DefaultImageName,
                DiagnosticsEngine &Diags)
   : Opts(createDriverOptTable()), Diags(Diags), Mode(GCCMode),
     ClangExecutable(ClangExecutable), SysRoot(DEFAULT_SYSROOT),
     UseStdLib(true), DefaultTargetTriple(DefaultTargetTriple),
-    DefaultImageName(DefaultImageName),
+    DefaultImageName("a.out"),
     DriverTitle("clang LLVM compiler"),
     CCPrintOptionsFilename(0), CCPrintHeadersFilename(0),
     CCLogDiagnosticsFilename(0),