make: Move lib make rules to src dir, consistency with meson build

src/makefile.mk

@@ -0,0 +1,35 @@
+#
+# Copyright 2022 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at:
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+liblc3_src += \
+    $(SRC_DIR)/attdet.c \
+    $(SRC_DIR)/bits.c \
+    $(SRC_DIR)/bwdet.c \
+    $(SRC_DIR)/energy.c \
+    $(SRC_DIR)/lc3.c \
+    $(SRC_DIR)/ltpf.c \
+    $(SRC_DIR)/mdct.c \
+    $(SRC_DIR)/plc.c \
+    $(SRC_DIR)/sns.c \
+    $(SRC_DIR)/spec.c \
+    $(SRC_DIR)/tables.c \
+    $(SRC_DIR)/tns.c
+
+liblc3_cflags += -ffast-math
+
+$(eval $(call add-lib,liblc3))
+
+default: liblc3