[RFC 2/2] Fold compat_symbol_unique functionality into compat_symbol

[Florian Weimer]

* Adhemerval Zanella:

> The __attribute__ ((nocommon)) on the malloc hook fixed the build issue.

I've fixed this locally, and also added to versioned_symbol:

   If LOCAL is a data symbol and does not have a non-zero initializer,
   it should be defined with __attribute__ ((nocommon)) for
   compatibility with GCC versions that default to -fcommon.  */

Should I posted a v3?

Thanks,
Florian