cmd/compile: fix type error reported on the wrong line

The 'Does not match' type error shoud be reported where
the function is called, not where the function is declared.

And fix the todo by gri of issue45985

Fixes #45985
Fixes #49800

Change-Id: I15aac44dd44f2a57c485a1c273fcd79db912c389
Reviewed-on: https://go-review.googlesource.com/c/go/+/362634


Reviewed-by: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>