busybox

Makefile: include per-arch Makefile before Makefile.flags

Makefile.flags contains:

ARCH_FPIC ?= -fpic
ARCH_FPIE ?= -fpie

However, arch/$(ARCH)/Makefile gets included *after* Makefile.flags,
and therefore doesn't get the chance to provide its own value.

Fix this by including arch/$(ARCH)/Makefile *before* Makefile.flags.

[Submitted upstream: http://lists.busybox.net/pipermail/busybox/2017-July/085632.html]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>