kbuild: stop filtering out $(GCC_PLUGINS_CFLAGS) from cc-option base

Commit d26e94149276 ("kbuild: no gcc-plugins during cc-option tests")
was neeeded because scripts/Makefile.gcc-plugins was too early.

This is unneeded by including scripts/Makefile.gcc-plugins last,
and being careful to not add cc-option tests after it.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
diff --git a/Makefile b/Makefile
index 483456d..7122063 100644
--- a/Makefile
+++ b/Makefile
@@ -506,7 +506,6 @@
 KBUILD_LDFLAGS_MODULE :=
 export KBUILD_LDS_MODULE := $(srctree)/scripts/module-common.lds
 KBUILD_LDFLAGS :=
-GCC_PLUGINS_CFLAGS :=
 CLANG_FLAGS :=
 
 export ARCH SRCARCH CONFIG_SHELL BASH HOSTCC KBUILD_HOSTCFLAGS CROSS_COMPILE LD CC
@@ -955,6 +954,10 @@
 
 include $(addprefix $(srctree)/, $(include-y))
 
+# scripts/Makefile.gcc-plugins is intentionally included last.
+# Do not add $(call cc-option,...) below this line. When you build the kernel
+# from the clean source tree, the GCC plugins do not exist at this point.
+
 # Add user supplied CPPFLAGS, AFLAGS and CFLAGS as the last assignments
 KBUILD_CPPFLAGS += $(KCPPFLAGS)
 KBUILD_AFLAGS   += $(KAFLAGS)