added avx/avx2 options via ROLLOPTS
added enable-avx option if requested by ROLLOPTS
added --host for cross compile
added "bash" in front of config.guess call
put --enable-avx in the right place
added config.guess call to v2.1.5
cleaned up AVX_FLAG stuff
changed make clean to make distclean between compiles for double and single precision
Merge pull request #3 in APS/fftw-roll from feature/APS-33-add-avx2-option-to-fftw-roll to master

* commit '8832331e9bec363d315169a3f935f537a9631dd1':
  changed make clean to make distclean between compiles for double and single precision
  cleaned up AVX_FLAG stuff
  added config.guess call to v2.1.5
  put --enable-avx in the right place
  added "bash" in front of config.guess call
  added --host for cross compile
  added enable-avx option if requested by ROLLOPTS
  added avx/avx2 options via ROLLOPTS