-fwhole-program and __attribute__((externally_visible))

[Joel Dice <dicej@xxxxxxxxxxxxx>]

Hi all,

I've been playing with -flto and -fwhole-program using an SVN snapshot of 
GCC and I have a couple of questions.

I'm using __attribute__((externally_visible)) to mark the entry points in 
my executable (which is also a shared object).  However, said attribute is 
not available with all versions of GCC.  What's the best way to determine 
whether it's available or not?

Also, I'm curious as to why above attribute is necessary at all.  All my 
code is built with -fvisibility=hidden, and the exported functions are 
marked with either __declspec(dllexport) or 
__attribute__((visibility("default"))), depending on the platform.  It 
seems redundant to specify an additional attribute that means essentially 
the same thing.

Thanks.