add host arch detection and Kconfig BR2_HOSTARCH

This will allow to install binary package only if they are supported by the
host. As example Atmel SAM-BA (x86 only).

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

Config.in

@@ -10,6 +10,10 @@ config BR2_VERSION
 	string
 	option env="BR2_VERSION_FULL"
 
+config BR2_HOSTARCH
+	string
+	option env="HOSTARCH"
+
 source "target/Config.in.arch"
 
 menu "Build options"

Makefile

@@ -32,6 +32,16 @@ ifneq ($(firstword $(sort $(MAKE_VERSION) $(MIN_MAKE_VERSION))),$(MIN_MAKE_VERSI
 $(error You have make '$(MAKE_VERSION)' installed. GNU make >= $(MIN_MAKE_VERSION) is required)
 endif
 
+export HOSTARCH := $(shell uname -m | \
+	sed -e s/i.86/x86/ \
+	    -e s/sun4u/sparc64/ \
+	    -e s/arm.*/arm/ \
+	    -e s/sa110/arm/ \
+	    -e s/ppc64/powerpc/ \
+	    -e s/ppc/powerpc/ \
+	    -e s/macppc/powerpc/\
+	    -e s/sh.*/sh/)
+
 # This top-level Makefile can *not* be executed in parallel
 .NOTPARALLEL: