selftests: add headers_install to lib.mk

If the kernel headers aren't installed we can't build all the tests.
Add a new make target rule 'khdr' in the file lib.mk to generate the
kernel headers and that gets include for every test-dir Makefile that
includes lib.mk If the testdir in turn have its own sub-dirs the
top_srcdir needs to be set to the linux-rootdir to be able to generate
the kernel headers.

Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
Reviewed-by: Fathi Boudra <fathi.boudra@linaro.org>
Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>
diff --git a/Makefile b/Makefile
index 2b45880..8b3fbdb 100644
--- a/Makefile
+++ b/Makefile
@@ -299,19 +299,7 @@
 KERNELVERSION = $(VERSION)$(if $(PATCHLEVEL),.$(PATCHLEVEL)$(if $(SUBLEVEL),.$(SUBLEVEL)))$(EXTRAVERSION)
 export VERSION PATCHLEVEL SUBLEVEL KERNELRELEASE KERNELVERSION
 
-# SUBARCH tells the usermode build what the underlying arch is.  That is set
-# first, and if a usermode build is happening, the "ARCH=um" on the command
-# line overrides the setting of ARCH below.  If a native build is happening,
-# then ARCH is assigned, getting whatever value it gets normally, and
-# SUBARCH is subsequently ignored.
-
-SUBARCH := $(shell uname -m | sed -e s/i.86/x86/ -e s/x86_64/x86/ \
-				  -e s/sun4u/sparc64/ \
-				  -e s/arm.*/arm/ -e s/sa110/arm/ \
-				  -e s/s390x/s390/ -e s/parisc64/parisc/ \
-				  -e s/ppc.*/powerpc/ -e s/mips.*/mips/ \
-				  -e s/sh[234].*/sh/ -e s/aarch64.*/arm64/ \
-				  -e s/riscv.*/riscv/)
+include scripts/subarch.include
 
 # Cross compiling and selecting different set of gcc/bin-utils
 # ---------------------------------------------------------------------------