Fix libswresample compilation with Apple Neon assembler.

Signed-off-by: Carl Eugen Hoyos <cehoyos@ag.or.at>
Merge remote-tracking branch 'cehoyos/master'

* cehoyos/master:
  Fix libswresample compilation with Apple Neon assembler.

Merged-by: Michael Niedermayer <michaelni@gmx.at>