kbuild: process mixture of clean/build targets one by one

Support parallel building of clean, config, and build targets in a
single command.

For example,

  make -j<N> clean all

or

  make -j<N> mrproper defconfig all

They should be handled one by one.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Makefile

@@ -220,7 +220,8 @@ export srctree objtree VPATH
 version_h := include/generated/uapi/linux/version.h
 old_version_h := include/linux/version.h
 
-no-dot-config-targets := clean mrproper distclean \
+clean-targets := %clean mrproper cleandocs
+no-dot-config-targets := $(clean-targets) \
 			 cscope gtags TAGS tags help% %docs check% coccicheck \
 			 $(version_h) headers_% archheaders archscripts \
 			 kernelversion %src-pkg
@@ -243,6 +244,14 @@ ifeq ($(KBUILD_EXTMOD),)
                 endif
         endif
 endif
+
+# For "make -j clean all", "make -j mrproper defconfig all", etc.
+ifneq ($(filter $(clean-targets),$(MAKECMDGOALS)),)
+        ifneq ($(filter-out $(clean-targets),$(MAKECMDGOALS)),)
+                mixed-targets := 1
+        endif
+endif
+
 # install and modules_install need also be processed one by one
 ifneq ($(filter install,$(MAKECMDGOALS)),)
         ifneq ($(filter modules_install,$(MAKECMDGOALS)),)