compiling skip on mac m1

[mpu]

To compile skip on a mac m1 I had to make the following two changes:

• In lkg/runtime/native/src/util.cpp, remove #include <xmmintrin.h>, comment out _mm_pause() further down.
• In src/runtime/native/src/util.cpp, do the same changes (not sure if that's of any use)

I also had to install via macports automake, libtool, autoconf.