testvlc: add missing bitstream.c
Fix unresolved symbol:
cc -o subprojects/dv/libdv/testvlc subprojects/dv/libdv/testvlc.p/testvlc.c.o subprojects/dv/libdv/testvlc.p/vlc.c.o subprojects/dv/libdv/testvlc.p/testvlc_x86_64.S.o -Wl,--as-needed -Wl,--no-undefined /usr/bin/ld: subprojects/dv/libdv/testvlc.p/testvlc.c.o: in function `bitstream_next_word':
subprojects/dv/libdv/bitstream.h:60: undefined reference to `_dv_bitstream_next_buffer'