[dev.link] cmd/link: use pclntabState and eliminate globals

[dev.link] cmd/link: use pclntabState and eliminate globals

Non functional change.

As runtime.pclntab breaks up, it'll be easier if we can just pass around
the pclntab state. Also, eliminate the globals in pclntab.

Change-Id: I2a5849e8f5f422a336a881e53a261e3997d11c44
Reviewed-on: https://go-review.googlesource.com/c/go/+/242599
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>