[LLVMdev] Fix crash in gold LTO plugin

[Nick Lewycky]

Todd Jackson wrote:
> While doing research using the LLVM link time optimizer, we discovered
> a bug in the LTO plugin.   After running the passes, the plugin tries to
> tell gold about 0 symbols produced from a bitcode file, indexing an
> empty vector in the expression&I->syms[0].  We're not completely sure
> if this is the best patch or if it is a symptom of a larger problem,
> but it worked for us.  When we found this, all of the input bitcode
> files had at least one symbol before running passes.
>
> The attached patch for 2.9 places a guard around the calls to the
> add_symbols plugin
> callback to only report symbols when the vector of symbols in the
> claimed_file is nonempty.
>
> Full credit for discovery and the patch goes to Jeffrey Bosboom.

Thanks! Fixed in r136066.

I chose to use if (...) continue; instead, just to keep the indentation 
depth low.

Nick