C++ makefile that auto finds source code in nested folders

Makefile

# C++ Flags
CPPFLAGS := -Wall -pedantic -g -std=c++17 # swap -g with -O3 and similar to release builds
CC := g++
LDLIBS := -lm -lstdc++ # libraries go here
INC := # includes go here

# General Notes:
#  - run $ make -j <num of cores on your machine>
# Expected file structure:
#  - Makefile
#  - src
#    - your-code.cpp
#    - some-dir
#			 - some-more-code.cpp
#
# Code and header files can be arbitrarely nested in the src folder
# the main function can be in any cpp file

BUILD_DIR := build
# ENDING is cpp, change to *.c++ if preferred
SRCS := $(shell find src -iname '*.cpp' -type f)
# Change *.h to *.hpp or *.h++ if your headers are named that
HEADERS := $(shell find src -iname '*.h' -type f)
OBJS := $(SRCS:src/%.cpp=$(BUILD_DIR)/%.o)
OUT := main # name of executable

.PHONY: clean lines run

# creates executable
$(OUT): $(OBJS)
	$(CC) -o $@ $^ $(LDLIBS)

# compile each source file
$(BUILD_DIR)/%.o: src/%.cpp $(HEADERS) 
	@mkdir -p $(@D)
	$(CC) -c $(INC) -o $@ $< $(CPPFLAGS)

# delete all generated files
clean:
	rm -rf $(BUILD_DIR) $(OUT)

# get line count of all sources and headers
lines: $(SRCS) $(HEADERS)
	wc -l $^ | grep total