/in/foo.c: In function 'main':
/in/foo.c:15:2: warning: implicit declaration of function 'ptintf' [-Wimplicit-function-declaration]
  ptintf("ckwckwckwckwckwckwckwckwckwckwckw\n");
  ^~~~~~
/tmp/ccU9HpBk.o: In function `main':
foo.c:(.text.startup+0xe): undefined reference to `ptintf'
foo.c:(.text.startup+0x1c): undefined reference to `ptintf'
foo.c:(.text.startup+0x2a): undefined reference to `ptintf'
foo.c:(.text.startup+0x38): undefined reference to `ptintf'
foo.c:(.text.startup+0x46): undefined reference to `ptintf'
/tmp/ccU9HpBk.o:foo.c:(.text.startup+0x54): more undefined references to `ptintf' follow
collect2: error: ld returned 1 exit status