include/cmake.mk: Add helper macro to handle conditionals for CMake boolean type variables

Signed-off-by: Vasilis Tsiligiannis <acinonyx@openwrt.gr>

SVN-Revision: 49164

include/cmake.mk

+cmake_bool = $(patsubst %,-D%:BOOL=$(if $($(1)),ON,OFF),$(2))
+
 PKG_INSTALL:=1
 
 ifneq ($(findstring c,$(OPENWRT_VERBOSE)),)