undefined reference to `pthread

I'm creating new threads in a function, and I've included pthread.h. But it's not working, I keep receiving the following error upon compiling:

undefined reference to `pthread_create'

The flags I'm using to compile are the following:

CFLAGS=-std=gnu99 -pthread -g -Wall -Wextra -Werror -Wmissing-declarations -Wmissing-prototypes -Werror-implicit-function-declaration -Wreturn-type -Wparentheses -Wunused -Wold-style-definition -Wundef -Wshadow -Wstrict-prototypes -Wswitch-default -Wunreachable-code

The compiler is gcc

Makefile:

CC=gcc
CFLAGS=-std=gnu99 -pthread -g -Wall -Wextra -Werror -Wmissing-declarations -Wmissing-prototypes -Werror-implicit-function-declaration -Wreturn-type -Wparentheses -Wunused -Wold-style-definition -Wundef -Wshadow -Wstrict-prototypes -Wswitch-default -Wunreachable-code

all: finder

finder: stack.o list.o finder.o
    $(CC) -o mfind stack.o list.o mfind.o

stack.o: stack.c stack.h
    $(CC) -c stack.c $(CFLAGS)

list.o: list.c list.h
    $(CC) -c list.c $(CFLAGS)

finder.o: finder.c finder.h
    $(CC) -c finder.c $(CFLAGS)

clean:
    rm -f *.o finder

---

-pthread is needed at the linking stage, not when compiling the individual translation units. A typical approach would look like this:

CC=gcc
CFLAGS=-std=gnu99 -g -Wall -Wextra -Werror -Wmissing-declarations -Wmissing-prototypes -Werror-implicit-function-declaration -Wreturn-type -Wparentheses -Wunused -Wold-style-definition -Wundef -Wshadow -Wstrict-prototypes -Wswitch-default -Wunreachable-code
LIBS=-pthread

all: finder

finder: stack.o list.o finder.o
    $(CC) -o mfind stack.o list.o mfind.o $(LIBS)

stack.o: stack.c stack.h
    $(CC) -c stack.c $(CFLAGS)

list.o: list.c list.h
    $(CC) -c list.c $(CFLAGS)

finder.o: finder.c finder.h
    $(CC) -c finder.c $(CFLAGS)

clean:
    rm -f *.o finder

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