compiler: check for floating-point exponent overflow

Adjust mksysinfo and mkrsysinfo to strip out floating-point max numbers,
as they can trigger this error.

Change-Id: If453722c6c149976f69a440d427180e810138326
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/278476
Trust: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
3 files changed