Revert "Fix compilation on ppc64 and ppc with pic if gas-preprocessor is installed."

It broke gas-preprocessor detection on PPC64 Linux.
This reverts commit b67bcd784dde7ad2b1a167ce7ffef14f8a0c8074.
avcodec/huffyuvdec: do not leave alpha values uninitialized

fixes fate failure under valgrind

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