[AIX] add -bdbg:namedsects:ss link arg

[daltenty]

On AIX, the PGO runtime and ifunc runtime support requires the named section linker feature which collects the name sections together and generates start/stop symbols for them.

This change adds the option to the default linker args for the target.

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[workingjubilee]

I see no significant reason to not simply r+ this aside from "is there any meaningful negative effect on linked executables and libraries when you're not doing PGO?"

This is just a small per-section binary size overhead, right?

And ifuncs? Defining new ifuncs, calling them, or both?

Happy to sign off on it either way if I understand correctly, just want to make sure I actually do.