cmd/compile: make map functions ABI insensitive

Following CL 309029, this CL does the same thing for map
functions (mapaccess, mapassign, mapdelete).

For simplicity, always wrap "defer delete(m, k)". With
regabidefers enabled, this call is wrapped in a closure and the
rewriting happens automatically. Without regabidefers, it may not
be wrapped for certain key types, and then we'd need special
handling of the delete (because earlier the order pass does not
handle it). And we will turn on defer wrapping by default anyway.

Change-Id: I30663b1aa8e1d6f98e1fb81bf8c0c0ce607ab80b
Reviewed-on: https://go-review.googlesource.com/c/go/+/309510


Trust: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>