Not on mac: a.c -> main; gcc -nostdlib -std=c89 a.c -o a a.c:1: warning: data definition has no type or storage class Undefined symbols for archit

Not on mac: a.c -> main; gcc -nostdlib -std=c89 a.c -o a a.c:1: warning: data definition has no type or storage class Undefined symbols for architecture x86_64: "start", referenced from: -u command line option ld: symbol(s) not found for architecture x86_64 collect2: ld returned 1 exit status`