kbuild: save overridden KERNELRELEASE in include/config/kernel.release

${KERNELRELEASE} is used as a part of the installation path.
(INSTALL_DTBS_PATH, MODLIB, etc.)

When KERNELRELEASE is overridden from the command line, it should be
saved in include/config/kernel.release, so that it will be consistently
used for the installation steps.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Makefile

@@ -1258,7 +1258,11 @@ vmlinux: vmlinux.o $(KBUILD_LDS) modpost
 # make sure no implicit rule kicks in
 $(sort $(KBUILD_LDS) $(KBUILD_VMLINUX_OBJS) $(KBUILD_VMLINUX_LIBS)): . ;
 
+ifeq ($(origin KERNELRELEASE),file)
 filechk_kernel.release = $(srctree)/scripts/setlocalversion $(srctree)
+else
+filechk_kernel.release = echo $(KERNELRELEASE)
+endif
 
 # Store (new) KERNELRELEASE string in include/config/kernel.release
 include/config/kernel.release: FORCE
@@ -2123,7 +2127,7 @@ checkstack:
 	$(PERL) $(srctree)/scripts/checkstack.pl $(CHECKSTACK_ARCH)
 
 kernelrelease:
-	@$(srctree)/scripts/setlocalversion $(srctree)
+	@$(filechk_kernel.release)
 
 kernelversion:
 	@echo $(KERNELVERSION)