nrf51822: test arguments for read/write even in stubs
nrf51822: Fix indentation in lpm_arch.c
nrf51822: error was not checked b/c of wrong signedness
nrf51822: Suppress unused argument warnings
dist/licenses: add and use diff-filter
dist/licenses: add and use --error-exitcode
Merge pull request #2072 from LudwigOrtmann/license-difffilter

dist/licenses: add and use diff-filter
cpu: added `extern "C"` to headers
Merge pull request #2078 from Kijewski/hello-world-warnings

nrf51822: hello-world builds without warnings
Merge pull request #1803 from BytesGalore/extern_C_in_headers_cpus

cpu: added `extern "C"` to headers