fpga: rfnoc: Add RFNoC Add/Sub block

Original-commit: 5134b6caea58da825c4da1888a4d26888acc126a

lib/rfnoc/blocks/rfnoc_block_addsub/Makefile.srcs

@@ -0,0 +1,22 @@
+#
+# Copyright 2020 Ettus Research, a National Instruments Brand
+#
+# SPDX-License-Identifier: LGPL-3.0-or-later
+#
+
+##################################################
+# RFNoC Block Sources
+##################################################
+# Here, list all the files that are necessary to synthesize this block. Don't
+# include testbenches!
+# Make sure that the source files are nicely detectable by a regex. Best to put
+# one on each line.
+# The first argument to addprefix is the current path to this Makefile, so the
+# path list is always absolute, regardless of from where we're including or
+# calling this file. RFNOC_OOT_SRCS needs to be a simply expanded variable
+# (not a recursively expanded variable), and we take care of that in the build
+# infrastructure.
+RFNOC_OOT_SRCS += $(addprefix $(dir $(abspath $(lastword $(MAKEFILE_LIST)))), \
+rfnoc_block_addsub.v \
+noc_shell_addsub.v \
+)