cmd/gc, cmd/ld: use content-addressable symbols for gclocals and gcargs #7568
Description
Poking through gc-produced binaries, there are a fair number of small symbols that represent the same data, particularly among gclocals.* and gcargs.*. Using dupok content-addressable symbols (like ARM does for floats and doubles, e.g. $f32.00000000) would allow many of these symbols to be gracefully collapsed, resulting in a smaller binary. It might even be worth having a general content-addressable symbol shared across all read-only users of small symbols. This might want to be controlled by a compiler flag, so that it is easy to separate back out the symbols as needed for debugging the liveness analysis, etc.