add prototype for escape-code function

src/libFLAC/include/private/bitbuffer.h

@@ -48,6 +48,7 @@ unsigned FLAC__bitbuffer_golomb_bits_signed(int val, unsigned parameter);
 unsigned FLAC__bitbuffer_golomb_bits_unsigned(unsigned val, unsigned parameter);
 bool FLAC__bitbuffer_write_symmetric_rice_signed(FLAC__BitBuffer *bb, int val, unsigned parameter);
 bool FLAC__bitbuffer_write_symmetric_rice_signed_guarded(FLAC__BitBuffer *bb, int val, unsigned parameter, unsigned max_bits, bool *overflow);
+bool FLAC__bitbuffer_write_symmetric_rice_signed_escape(FLAC__BitBuffer *bb, int val, unsigned parameter);
 bool FLAC__bitbuffer_write_rice_signed(FLAC__BitBuffer *bb, int val, unsigned parameter);
 bool FLAC__bitbuffer_write_rice_signed_guarded(FLAC__BitBuffer *bb, int val, unsigned parameter, unsigned max_bits, bool *overflow);
 bool FLAC__bitbuffer_write_golomb_signed(FLAC__BitBuffer *bb, int val, unsigned parameter);