A first stab at position independent code generation for i386-linux.
It doesn't work yet, but it shouldn't break anything.

What we need now is one or both of the following:
a) A volunteer to implement PIC for x86 -fvia-C
    (I definitely refuse to touch any piece of code that contains
     both Perl and x86 assembly).
b) A volunteer to improve the NCG to the point where it can compile
   the RTS (so we won't need point a).