Minor feature for ld

[DJ Delorie]

> You can still do this... you need to define types for the variables in
> a header, and declare them as "extern", then define them to the right
> address in a linker script.  No need to use sections at all.

You don't even need a linker script.  You can do it in assembler, and
compile+link like any other source file:

	.global	REG_BG2CNT
REG_BG2GNT = 0x400000C

Watch out for leading underscores if your platform needs them, of
course.