Register Allocator Bug

[Wolfgang Thaller]

On x86-linux, with the latest HEAD, the following code triggers a 
register allocation bug:

#include "Cmm.h"
foo {
        I32 bar;                                // bar get's assigned to %eax
        foreign "C" bar ();   // %eax is correctly saved accross this call
        foreign "C" bar ();   // But this call clobbers it.
        jump bar;                               // here we'll probably crash.
}
This gets compiled to:
.text
        .align 4,0x90
.globl foo
foo:
        movl %esi,%eax
        movl %eax,64(%esp)
        call *%eax
        addl $0,%esp
        movl 64(%esp),%eax
        call *%eax
        addl $0,%esp
        jmp *%eax
As you can see, %eax isn't restored between the second call and the 
jump.
This bug prevents me from finding any further problems with the PIC 
support I
just comitted :-).

Cheers,
Wolfgang
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