int 0x80 is legacy, and x86, but it isn't specific to Linux.
FreeBSD (and AFAIK other BSDs) also use(d) it; most likely any Unix system on x86 that doesn't require a processor with sysenter/syscall instructions would use int 0x80 to do syscalls.
According to this stackoverflow answer, "int 0x80" is a Linux-specific legacy way to do syscalls:
https://stackoverflow.com/questions/12806584/what-is-better-...