[gcov] Simplify file interface

[Jan Hubicka]

> This patch simplifies the gcov file interface. The original interface
> was designed around FILE, but Zdenek Dvorak found a problem with
> the seeks performed that caused excessive disk activity. He implemented
> a buffer based interface behind the FILE interface. That overly complicates
> things, and has excessive copying.
> 
> This patch removes the FILE interface, and makes the gcov file access work
> one file at a time (the runtime already did this, but the compiler
> did not). IMO this makes the interface much simpler.
> 
> In profile.c I now read in and merge the appropriate counts in one go,
> rather than index the gcov file and then gather the statistics as necessary.
> 
> I also corrected some errors with Zdenek's patch, it incorrectly accumulated
> PROGRAM_SUMMARY data, and would open binary files not in text mode.
> 
> The patch is obvious, once one has bought into removing the FILE interface.
> It shaves about 2 minutes of a --enable-coverage bootstrap and 1/3 off a
> subsequent check-gcc & check-g++.

Sounds cool.  You also may like to play around with my profiledbootstrap
patch, that gives additional checking to the profile code.  I would like
to hear your opionion about that - I am quite unsure about the Makefile
stuff.

Honza