kconfig: print more info when we see a recursive dependency

Consider following kconfig file:

config TEST1
	bool "test 1"
	depends on TEST2

config TEST2
	bool "test 2"
	depends on TEST1

Previously kconfig would report:

foo:6:error: found recursive dependency: TEST2 -> TEST1 -> TEST2

With the following patch kconfig reports:
foo:5:error: recursive dependency detected!
foo:5:  symbol TEST2 depends on TEST1
foo:1:  symbol TEST1 depends on TEST2

Note that we now report where the offending symbols are defined.
This can be a great help for complex situations involving
several files.

Patch is originally from Roman Zippel with a few adjustments by Sam.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>