[patch] add support for PIC on linux x86-64

The attached patch adds support for PIC on linux x86-64. It also adds
some tests. The patch fixes tests 1, 10 and 11. I would like to keep
all tests, since I find the assembler printer code a bit hard to read,
and I like to have tests around to find out if a change does what I
think it does.

With this patch I was able to bootstrap gcc in linux x86-64 with
shared libraries enabled :slight_smile:

Cheers,