math: handle real_absolute variables more accurately

math: handle real_absolute variables more accurately

The problem here is that we were either using smatch_extra or
real_absolute.  Say you code like this:

	int x = (u8)unknown_variable;

	if (x > 10)
		return;
	__smatch_about(x);

In this example, the "x = (u8)unknown_variable;" assignment is ignored by
smatch_extra because we know literally nothing about unknown_variable, but
it's stored as x = 0-255 in real_absolute.

Then when we get to the condition "if (x > 10)" we say in smatch_extra.c
that x is now s32min-10.  So now when we query the real absolute value we
use the smatch_extra data instead of the real_absolute.

Hm...  Writing this patch description, it makes me wonder why the
handle_comparison() handling code in smatch_extra.c doesn't use the
real_absolute?  It get_real_absolute_rl() at the start already...

None the less, this change makes sense all on its own.  What we do now is
that we take the smatch_extra value and the real_absolute value and use
the intersection of both.

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