comparison: handle merging comparisons

comparison: handle merging comparisons

This is a pretty involved patch.  Theoretically I could have broken it up
into two parts, but when I'm coding my own stuff then I have no standards
so it's all going in as one big patch.

The code we care about looks like this:

	if (x < 10)
		y = x;
	else
		y = 10;
	__smatch_compare(x, y);

On the first branch y == x.  On the second branch we wouldn't normally
store the relationship between x and y so we have an unmatched state.  We
can determine the relationship though.  Then we merge the states together
to get the final relationship.

The first thing to say is that smatch_compare.c didn't used to store the
name and symbols of the variables being compared.  So I had to create a
dynamically allocated smatch_state so that information could be stored in
the ->data.

The next part of the change is if there is an unmatched state.  We can get
the implied range list for both variables and determine the relationship
from that.  y is 10.  x is 10-max.  That means y <= x.

Then when we merge it it's simple enough y == x and y <= x combine to say
that y <= x.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>