avcodec/x86/h264_qpel_10bit: locally define pb_0

somehow old llvm-gcc manages to ignore the alignment from ff_pb_0 causing a crash on freebsd
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/x86/h264_qpel_10bit.asm

@@ -28,7 +28,7 @@ SECTION_RODATA 32
 
 cextern pw_16
 cextern pw_1
-cextern pb_0
+pb_0: times 32 db 0 ; we do not use cextern here as old llvm-gcc fails to align it correctly
 
 pw_pixel_max: times 8 dw ((1 << 10)-1)