base: ld-<platform>.abi.so depends on symbol.map

This prevents errors like the following during parallel builds.

      MERGE    ld-hw.abi.so
  /usr/local/genode/tool/21.05/bin/genode-arm-ld:symbol.map:0: syntax error in VERSION script

repos/base/lib/mk/ld-platform.inc

@@ -20,6 +20,7 @@ SYMBOLS := $(BASE_DIR)/lib/symbols/ld
 # Generate symbol map from the ABI
 #
 $(LIB).lib.so: symbol.map
+$(LIB).abi.so: symbol.map
 symbol.map: $(MAKEFILE_LIST)
 symbol.map: $(BASE_DIR)/lib/symbols/ld
 	$(MSG_CONVERT)$@