driver: enable -use-dwarf-debug-flags

[compnerd]

Summary

This changes the default to embed the -cc1 flags into the emitted object files.

[dblaikie]

Test case?
Impact assessment? (how much does this grow LLVM's debug info by, for example?)

[echristo]

Not expecting it to be much, but hopefully you don't mean -cc1 options but rather "options passed to the compiler"?

[echristo]

What's going on with this? I'm not against the idea, but it needs testing and an answer to my question :)

[compnerd]

Wow, I completely forgot about this patch. Yes, I mean the options passed to the compiler. Ill certainly add a test case.

[compnerd]

As for the question on the size difference:

@dblakie, the overall build is nearly 1M larger (I forgot to measure the size of the binary itself, if thats what you were interested in).

include/clang/Driver/ToolChain.h

 
   /// UseDwarfDebugFlags - Embed the compile options to clang into the Dwarf
   /// compile unit information.
-  virtual bool UseDwarfDebugFlags() const { return false; }
+  virtual bool UseDwarfDebugFlags() const { return true; }
 
   /// UseSjLjExceptions - Does this tool chain use SjLj exceptions.
   virtual bool UseSjLjExceptions() const { return false; }

test/Driver/debug-flags.c

+// RUN: %clang -### -target i686-linux-gnu -c %s -o /dev/null 2>&1 | FileCheck %s
+
+// CHECK: -dwarf-debug-flags
+