[committed] Fix frv build after C99 changes

[committed] Fix frv build after C99 changes

Two issues prevent the frv-elf port from building after the C99 changes.  First
the trampoline code emitted into libgcc has calls to exit, but no prototype.
Adding a trivial prototype for exit() into the macro fixes that little goof.

Second, frvbegin.c has a call to atexit, so a quick prototype is added into
frvbegin.c to fix that problem.

That's enough to get the compiler building again.

gcc/
	* config/frv/frv.h (TRANSFER_FROM_TRAMPOLINE): Add prototype for exit.

libgcc/
	* config/frv/frvbegin.c (atexit): Add prototype.