utils: Fixes grcc to exit with an error code in case of a compilation error.
runtime: Fixed runtime SWIG linker error

* gnuradio_runtime_EXPORTS is not defined for SWIG builds by default, so this fix manually sets it for the runtime_swig build
Merge remote-tracking branch 'ncorgan/runtime_swig_fix' into maint
volk: tests if xgetbv (an avx instruction) is really, truly available. Allows us to build on OSX with GCC.
volk: update QA test to use non integer multiples of register sizes to ensure we test the tail cases.
volk: update Volk profiker to use non integer multiples of register sizes to ensure we profile the tail cases.
modtool: forces another check for include dirs and libraries when looking for gnuradio-runtime. Similar to how GnuradioConfig.cmake looks for components.
digital: fix for moving average filter in OFDM equalizer.