[gcov] Simplify read/write functions

[Jan Hubicka]

> Hi,
> This patch simplifies the gcov data marshalling interface. Rather
> than return an error code, we have a sticky global error flag. This
> allows us to simply return the read values, rather than have a pointer
> parameter.
> 
> This change reduces the (i86) text size of libgcov from 6306 bytes to
> 5810 bytes (not that that was the primary goal of this patch).

This looks fine to me :).  Reducing the size would get us nearer to
possible use in embedded environments.

Do you have some futher changes to the area in queue?  If not, I will
probably update my patch to avoid second pass and kill the max_sum
field so we will be able to use gcov in parallel make environment.
Looks like sane plan?

Honza