kbuild: $(CHECK) doesnt need NOSTDINC_FLAGS twice

Currently, $(CHECK) receives NOSTDINC_FLAGS twice:
* first directly in the main Makefile via CHECKFLAGS,
* then indirectly in scripts/Makefile.build via c_flags.

Since once is enough, leave the occurence via c_flags and
remove the one via CHECKFLAGS.
Signed-off-by: NLuc Van Oostenryck <luc.vanoostenryck@gmail.com>
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>

Makefile

@@ -805,7 +805,6 @@ endif
 
 # arch Makefile may override CC so keep this after arch Makefile is included
 NOSTDINC_FLAGS += -nostdinc -isystem $(call shell-cached,$(CC) -print-file-name=include)
-CHECKFLAGS     += $(NOSTDINC_FLAGS)
 
 # warn about C99 declaration after statement
 KBUILD_CFLAGS += $(call cc-option,-Wdeclaration-after-statement,)