Compound Literals with ARMCC: or what does '--gnu'?

I'd like to use compound literals.
So as I found in uVision help that if we use --gnu as additional compiler string, this C99 functionality is given.

int y[] = (int []) {1, 2, 3}; // error in strict C99, okay in C99 --gnu
int z[] = (int [3]) {1};

Now, I get a lot of linker warnings: multiple defines of a lot of inline function declared in lib_AT91SAM7X512.h
It's a pain that keil distributes these device-header files with code inside the header file.
How can i get it linking with --gnu option? General: What does --gnu do exactly? It is still ARMCC taken.
Or how do I get my compound literals compiled with normal compiler settings (ARMCC)?

Thanks for your help in advance.