Handle correctly global0 and global counters in profile_count::to_sreal_scale

Handle correctly global0 and global counters in profile_count::to_sreal_scale

This patch fixes problem in profile_count::to_sreal_scale.  We our porfile
counters can be function local, global (ipa) or function local but globally 0.
The last is used to hold static estimates for functions executed 0 times in
profile.  Now only one 64bit value is stored and if we compute frequency
of global0 counter in global counter we mix them up and return non-zero value
incorrectly.

I also implemented unit test, but will commit sanity checking separately from
fixes: there are multiple bugs in this area I tracked down.

	* profile-count.c (profile_count::to_sreal_scale): Handle correctly
	combination of globa0 and global counters..

From-SVN: r278801