[PATCH 2/4] gas: Add support for LLVM addrsig and addrsig_sym directives on ELF.

[Tatsuyuki Ishi]

> Why two directives? IOW what's the point of silently ignoring
> .addrsig_sym when there's no .addrsig anywhere?

Because addrsig is an opt-in mechanism. A file with only .addrsig means that
none of the symbols are address significant, while a file without is treated
as if all symbols were.

The silent ignore behavior is not ideal, but it could be added later. The
primary target of this patch is compiler generated output.

> And such a toggle-on
> directive likely would want to allow expressing also (or even only)
> via a command line option.

How would that work? That leads to two kind of end results, 1. mark *all*
symbols as address-insignificant (if there's no addrsig_sym directives)
or maybe 2. toggle off llvm_addrsig support (but why?).