Describing what patches do

From: Ákos Kovács <[email protected]>

Patch 1:
Add new logical functions to rules.mak, to eliminate and simplify variables in the Makefiles.

Example usage:
obj-$(call lor,$(CONFIG_LINUX),$(CONFIG_BSD)) += feature.o

Patch 2:
Remove CONFIG_GDBSTUB_XML from default_configs/*.mak files and make a new rule (in Makefile.target) to build the gdbstub_xml object, with the new logical functions from the first patch.

Patch 3:
Remove CONFIG_NO_* variables from Makefile.target. And replace their uses with the negation of the corresponding variable.