Allow override of device asserts, including multi-device support.

Set in board file with TARGET_OTA_ASSERT_DEVICE.
(cherry-picked from commit 0f452f2)

Change-Id: I3d06bdc0e3e26bde0c0e646accd050364f9713b9
add no_assets.option
Change-Id: I489e7b965aa2e4286ebacd64006522a5d206f2db
test -O2 flag
Use linaro-4.7 toolchain

Change-Id: I88f7bacba70472538e98450ec46afd477fa04f0a
pesky line!

- fixes apns distinguish issues
build: fix target header overlay

LOCAL_C_INCLUDES as defined by the makefile should be put AFTER
the overlay includes so the overlay always takes precedence.

Change-Id: I489b2aab6dbacd9122d834f85e07b63ed1271f07