Now all warnings are disabled on SDK files, and enabled on our
application's files.
Fixed a couple of things in nRF52 which were unnoticed because all
warnings were disabled there from the beginning.
PUBLISHED_FROM=a33ab22d0ce85efea364b80478986b88f4b0a3a2
Unfortunately it turns out Nordic's examples were able to build with GCC
just because they suppressed all warnings; I had to do the same here
because there are some macro redefinitions of arm-none-eabi-gcc and
lwip.
TODO: resolve that and do not suppress warnings.
PUBLISHED_FROM=e65c7b0f2451f85765d958d7f67eb9262f7bc929