kbuild: add outputmakefile to no-dot-config-targets

The target outputmakefile is used to generate a Makefile
for out-of-tree builds and does not depend on the kernel
configuration.
Signed-off-by: David Engraf <david.engraf@sysgo.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Makefile

@@ -255,7 +255,8 @@ clean-targets := %clean mrproper cleandocs
 no-dot-config-targets := $(clean-targets) \
 			 cscope gtags TAGS tags help% %docs check% coccicheck \
 			 $(version_h) headers headers_% archheaders archscripts \
-			 %asm-generic kernelversion %src-pkg dt_binding_check
+			 %asm-generic kernelversion %src-pkg dt_binding_check \
+			 outputmakefile
 no-sync-config-targets := $(no-dot-config-targets) install %install \
 			   kernelrelease
 single-targets := %.a %.i %.ko %.lds %.ll %.lst %.mod %.o %.s %.symtypes %/