Add ARCH variable to Makefiles

In some Makefiles the ARCH variable was not set, although it was used.
In executer/user/Makefile.in it was used before it was set.

kernel/Makefile.build.in

@@ -1,4 +1,5 @@
 # Makefile.build.in COPYRIGHT FUJITSU LIMITED 2015-2016
+ARCH = @ARCH@
 VPATH=@abs_srcdir@
 SRC=$(VPATH)
 IHKDIR=$(IHKBASE)/$(TARGETDIR)
@@ -37,7 +38,7 @@ OBJCOPY ?= objcopy
 
 # POSTK_DEBUG_ARCH_DEP_26
 ifeq ($(ARCH), arm64)
-SUBCMD_OPTS = TARGET=$(TARGET) O=$(CURDIR)/ihk CC=$(CC) LD=$(LD) OBJCOPY=$(OBJCOPY) SRC=$(SRC)
+SUBCMD_OPTS = TARGET=$(TARGET) O=$(CURDIR)/ihk CC=$(CC) LD=$(LD) OBJCOPY=$(OBJCOPY) SRC=$(SRC) ARCH=$(ARCH)
 else
 SUBCMD_OPTS = TARGET=$(TARGET) O=$(CURDIR)/ihk CC=$(CC) LD=$(LD) SRC=$(SRC)
 endif

kernel/Makefile.in

@@ -1,6 +1,7 @@
 BUILD_TARGET ?= @TARGET@
 KERNDIR=@KERNDIR@
 VPATH=@abs_srcdir@
+ARCH ?= @ARCH@
 
 ifeq ($(ARCH), arm64)
 vdsodir=@abs_builddir@/../arch/$(ARCH)/kernel/vdso