cmd/internal/obj/x86: better error msg for offset overflow on AMD64

cmd/internal/obj/x86: better error msg for offset overflow on AMD64

Say "offset too large" instead of "invalid instruction" when
assembling for AMD64. GOARCH=386 already reports error correctly.

Fixed #24871

Change-Id: Iab029307b5c5edbb45f9df4b64c60ecb5f101349
Reviewed-on: https://go-review.googlesource.com/107116
Run-TryBot: Iskander Sharipov <iskander.sharipov@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>