kbuild: Send various piping stderr stream output to /dev/null

- This suppresses following errors for us:

  error: write on a pipe with no reader

- Fix references are from issue ClangBuiltLinux/linux#1651

Co-authored-by: GhostMaster69-dev <rathore6375@gmail.com>
Signed-off-by: GhostMaster69-dev <rathore6375@gmail.com>
[Diaz1401: also apply on cmd_modversions_S]
Signed-off-by: Diaz1401 <reagor8161@outlook.com>

scripts/Makefile.build

@@ -195,20 +195,20 @@ ifdef CONFIG_LTO_CLANG
 # to the kernel and/or modules at the end.
 cmd_modversions_c =								\
 	if $(OBJDUMP) -h $(@D)/.tmp_$(@F) >/dev/null 2>/dev/null; then		\
-		if $(OBJDUMP) -h $(@D)/.tmp_$(@F) | grep -q __ksymtab; then	\
+		if $(OBJDUMP) -h $(@D)/.tmp_$(@F) 2>/dev/null | grep -q __ksymtab; then	\
 			$(call cmd_gensymtypes_c,$(KBUILD_SYMTYPES),$(@:.o=.symtypes)) \
 			    > $(@D)/$(@F).symversions;				\
 		fi;								\
 	else									\
-		if $(LLVM_NM) $(@D)/.tmp_$(@F) | grep -q __ksymtab; then	\
+		if $(LLVM_NM) $(@D)/.tmp_$(@F) 2>/dev/null | grep -q __ksymtab; then	\
 			$(call cmd_gensymtypes_c,$(KBUILD_SYMTYPES),$(@:.o=.symtypes)) \
 			    > $(@D)/$(@F).symversions;				\
 		fi;								\
 	fi;									\
 	mv -f $(@D)/.tmp_$(@F) $@;
 else
 cmd_modversions_c =								\
-	if $(OBJDUMP) -h $(@D)/.tmp_$(@F) | grep -q __ksymtab; then		\
+	if $(OBJDUMP) -h $(@D)/.tmp_$(@F) 2>/dev/null | grep -q __ksymtab; then		\
 		$(call cmd_gensymtypes_c,$(KBUILD_SYMTYPES),$(@:.o=.symtypes))	\
 		    > $(@D)/.tmp_$(@F:.o=.ver);					\
 										\
@@ -421,7 +421,7 @@ else
 cmd_as_o_S = $(CC) $(a_flags) -c -o $(@D)/.tmp_$(@F) $<
 
 cmd_modversions_S =								\
-	if $(OBJDUMP) -h $(@D)/.tmp_$(@F) | grep -q __ksymtab; then		\
+	if $(OBJDUMP) -h $(@D)/.tmp_$(@F) 2>/dev/null | grep -q __ksymtab; then		\
 		$(call cmd_gensymtypes_S,$(KBUILD_SYMTYPES),$(@:.o=.symtypes))	\
 		    > $(@D)/.tmp_$(@F:.o=.ver);					\
 										\