Fix compilation on powerpc with --disable-altivec

in case altivec is disabled, even compilation of code using altivec
keywords or asm must be avoided.

backport r30869 from mplayer repo by siretart


Originally committed as revision 22436 to svn://svn.ffmpeg.org/ffmpeg/branches/0.5

libswscale/swscale.c

@@ -960,7 +960,7 @@ static inline void yuv2rgbXinC_full(SwsContext *c, int16_t *lumFilter, int16_t *
 #endif
 
 #if ARCH_PPC
-#if HAVE_ALTIVEC || CONFIG_RUNTIME_CPUDETECT
+#if HAVE_ALTIVEC
 #define COMPILE_ALTIVEC
 #endif
 #endif //ARCH_PPC
@@ -1649,7 +1649,7 @@ static SwsFunc getSwsFunc(int flags){
         return swScale_C;
 
 #else
-#if ARCH_PPC
+#if ARCH_PPC && COMPILE_ALTIVEC
     if (flags & SWS_CPU_CAPS_ALTIVEC)
         return swScale_altivec;
     else