* sysdeps/unix/sysv/linux/kernel-features.h (__ASSUME_VFORK_SYSCALL):
Define for 2.4+ kernels.
* sysdeps/unix/sysv/linux/i386/vfork.S: Optimize for kernels which
are known to have the vfork syscall. Don't confuse the CPUs
branch prediction unit by jumping to the return address.