PPC: fix build on OSX without gas-preprocessor

Originally committed as revision 23962 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/ppc/fft_altivec.c

@@ -196,9 +196,9 @@ static void ff_imdct_calc_altivec(FFTContext *s, FFTSample *output, const FFTSam
 
 av_cold void ff_fft_init_altivec(FFTContext *s)
 {
-    if (HAVE_GNU_AS) {
+#if HAVE_GNU_AS
     s->fft_calc = ff_fft_calc_altivec;
     s->imdct_calc = ff_imdct_calc_altivec;
     s->imdct_half = ff_imdct_half_altivec;
-    }
+#endif
 }