make test_barriers
cc     test_barriers.c   -o test_barriers
/tmp/ccYk6FDO.o: In function `test_barriers_linear_array':
test_barriers.c:(.text+0x610): undefined reference to `pthread_create'
test_barriers.c:(.text+0x68c): undefined reference to `pthread_create'
test_barriers.c:(.text+0x756): undefined reference to `pthread_join'
/tmp/ccYk6FDO.o: In function `test_barriers_variables':
test_barriers.c:(.text+0xe08): undefined reference to `pthread_create'
test_barriers.c:(.text+0xe86): undefined reference to `pthread_create'
test_barriers.c:(.text+0xf53): undefined reference to `pthread_join'
/tmp/ccYk6FDO.o: In function `test_barriers_scattered_array':
test_barriers.c:(.text+0x1322): undefined reference to `pthread_create'
test_barriers.c:(.text+0x13a0): undefined reference to `pthread_create'
test_barriers.c:(.text+0x146d): undefined reference to `pthread_join'
collect2: ld returned 1 exit status
make: *** [test_barriers] Error 1