Makefile: Introduce per-file CFLAGS removal.

This adds the reverse of CFLAGS_obj.o with CFLAGS_REMOVE_obj.o.
This allows to prevent certain CFLAGS from being used to
compile files.

travis-ci: success for series starting with [1/6] compel/infect: fix out-of-bounds parasite memcpy()
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Safonov <dsafonov@virtuozzo.com>
Reviewed-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

scripts/nmk/scripts/build.mk

@@ -43,7 +43,7 @@ LDFLAGS		:= $(filter-out $(LDFLAGS-MASK),$(LDFLAGS))
 #
 # Accumulate common flags.
 define nmk-ccflags
-        $(CFLAGS) $(ccflags-y) $(CFLAGS_$(@F))
+        $(filter-out $(CFLAGS_REMOVE_$(@F)), $(CFLAGS) $(ccflags-y) $(CFLAGS_$(@F)))
 endef
 
 define nmk-asflags