kbuild: hide error checker logs for V=1 builds

V=1 (verbose build) shows commands executed by Make, but it may cause
misunderstanding.

For example, the following command shows the outstanding error message.

  $ make V=1 INSTALL_PATH=/tmp install
  test -e include/generated/autoconf.h -a -e include/config/auto.conf || (                \
  echo >&2;                                                       \
  echo >&2 "  ERROR: Kernel configuration is invalid.";           \
  echo >&2 "         include/generated/autoconf.h or include/config/auto.conf are missing.";\
  echo >&2 "         Run 'make oldconfig && make prepare' on kernel src to fix it.";      \
  echo >&2 ;                                                      \
  /bin/false)
    unset sub_make_done; ./scripts/install.sh

It is not an error. Make just showed the recipe lines it has executed,
but people may think that 'make install' has failed.

Likewise, the combination of V=1 and O= shows confusing
"*** The source tree is not clean, please run 'make mrproper'".

Suppress such misleading logs.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

Makefile

@@ -583,7 +583,7 @@ quiet_cmd_makefile = GEN     Makefile
 	} > Makefile
 
 outputmakefile:
-	$(Q)if [ -f $(srctree)/.config -o \
+	@if [ -f $(srctree)/.config -o \
 		 -d $(srctree)/include/config -o \
 		 -d $(srctree)/arch/$(SRCARCH)/include/generated ]; then \
 		echo >&2 "***"; \
@@ -736,7 +736,7 @@ else # !may-sync-config
 PHONY += include/config/auto.conf
 
 include/config/auto.conf:
-	$(Q)test -e include/generated/autoconf.h -a -e $@ || (		\
+	@test -e include/generated/autoconf.h -a -e $@ || (		\
 	echo >&2;							\
 	echo >&2 "  ERROR: Kernel configuration is invalid.";		\
 	echo >&2 "         include/generated/autoconf.h or $@ are missing.";\