multimedia/mlt7: fix build with lld 17

Building multimedia/mlt7 with lld 17 results in the following link
errors:

  ld: error: version script assignment of 'MLT_0.8.8' to symbol 'mlt_frame_get_alpha_mask' failed: symbol not defined
  ld: error: version script assignment of 'MLT_0.8.8' to symbol 'mlt_geometry_close' failed: symbol not defined
  ld: error: version script assignment of 'MLT_0.8.8' to symbol 'mlt_geometry_fetch' failed: symbol not defined
  ld: error: version script assignment of 'MLT_0.8.8' to symbol 'mlt_geometry_get_length' failed: symbol not defined
  ld: error: version script assignment of 'MLT_0.8.8' to symbol 'mlt_geometry_init' failed: symbol not defined
  ld: error: version script assignment of 'MLT_0.8.8' to symbol 'mlt_geometry_insert' failed: symbol not defined
  ld: error: version script assignment of 'MLT_0.8.8' to symbol 'mlt_geometry_interpolate' failed: symbol not defined
  ld: error: version script assignment of 'MLT_0.8.8' to symbol 'mlt_geometry_next_key' failed: symbol not defined
  ld: error: version script assignment of 'MLT_0.8.8' to symbol 'mlt_geometry_parse' failed: symbol not defined
  ld: error: version script assignment of 'MLT_0.8.8' to symbol 'mlt_geometry_parse_item' failed: symbol not defined
  ld: error: version script assignment of 'MLT_0.8.8' to symbol 'mlt_geometry_prev_key' failed: symbol not defined
  ld: error: version script assignment of 'MLT_0.8.8' to symbol 'mlt_geometry_refresh' failed: symbol not defined
  ld: error: version script assignment of 'MLT_0.8.8' to symbol 'mlt_geometry_remove' failed: symbol not defined
  ld: error: version script assignment of 'MLT_0.8.8' to symbol 'mlt_geometry_serialise' failed: symbol not defined
  ld: error: version script assignment of 'MLT_0.8.8' to symbol 'mlt_geometry_serialise_cut' failed: symbol not defined
  ld: error: version script assignment of 'MLT_0.8.8' to symbol 'mlt_geometry_set_length' failed: symbol not defined
  ld: error: version script assignment of 'MLT_0.8.8' to symbol 'mlt_playlist_move_region' failed: symbol not defined
  ld: error: version script assignment of 'MLT_0.8.8' to symbol 'mlt_sample_calculator' failed: symbol not defined
  ld: error: version script assignment of 'MLT_0.8.8' to symbol 'mlt_sample_calculator_to_now' failed: symbol not defined
  ld: error: version script assignment of 'MLT_0.9.10' to symbol 'mlt_properties_to_utf8' failed: symbol not defined

Add -Wl,--undefined-version to LDFLAGS to suppress these errors, since
mlt7 has several symbols that are defined conditionally (depending on
the target platform).

PR:		273753
MFH:		2023Q4

multimedia/mlt7/Makefile

@@ -17,6 +17,9 @@ USES+=			alias cmake compiler:c++11-lang eigen:3 localbase \
 			pathfix pkgconfig
 USE_LDCONFIG=		yes
 
+# Suppress errors with lld >= 17 due to undefined symbols.
+LDFLAGS+=		-Wl,--undefined-version
+
 DATADIR=		${PREFIX}/share/mlt-7
 
 .ifndef(SLAVEPORT) # Master port.