Minor feature for ld

[Pete Gonzalez]

I think the linker should support segments whose address is a
function of the segment name.  It would allow definitions like
this in GCC:

   __attribute__((section("/0x123456/"))) int IOPort;

In the above example, the linker would locate the variable at
the given address, so these two statements would be equivalent:

   IOPort = x;
   *(int *)0x123456 = x;

Really this feature belongs in the compiler, but sections are
the closest C/C++ compilers come to letting you control the
address of variables.  Everything else is handled by the linker,
so that seems like the simplest place to fix.  (If not, maybe
I should be pestering the GCC people.)

Thanks,
-Pete