/tmp/ccekp0RG.o: In function `main':
foo.cc:(.text.startup+0x78): undefined reference to `gcd(int, int)'
foo.cc:(.text.startup+0x87): undefined reference to `gcd(int, int)'
foo.cc:(.text.startup+0x97): undefined reference to `gcd(int, int)'
collect2: error: ld returned 1 exit status