sysenter on x86

[Felix von Leitner]

I just added sysenter support for linux-2.5 on x86 to the diet libc, but
I noted that the original patch said user space should jump to
0xfffff000, which segfaults.  Jumping to 0xffffe000 works.

I suggest adding a comment somewhere in the kernel about the proper
calling convention, because the glibc code is frankly not readable in
this regard.

Also, I suggest adding this interface to kernel 2.4 to easy binary
compatibility.

Felix