[dev.link] cmd/link: add new slice interface for querying aux symbols
Add a new loader.Loader.ReadAuxSyms method that returns a slice
containing the ids of the aux symbols for a specified global symbol.
This is similar to the new interface recently added that allows you to
get back a slice of relocations (as opposed to making calls into the
loader for each one). This was idea suggested by Cherry. Compilebench
numbers:
name old time/op new time/op delta
LinkCompiler 1.63s ± 9% 1.57s ± 7% -3.84% (p=0.006 n=20+20)
LinkWithoutDebugCompiler 1.15s ±11% 1.11s ±11% ~ (p=0.108 n=20+20)
name old user-time/op new user-time/op delta
LinkCompiler 1.99s ± 8% 2.00s ±12% ~ (p=0.751 n=19+19)
LinkWithoutDebugCompiler 1.14s ±11% 1.19s ±21% ~ (p=0.183 n=20+20)