There may be gaps between non-writeable and writeable PT_LOAD
segments, and the gaps may be large as the segments may have
large alignment. Don't count those gaps in file size comparison.

Fixes #36023.

Change-Id: I68582bdd0f385ac5c6f87d485d476d06bc96db19
Reviewed-on: https://go-review.googlesource.com/c/go/+/210180
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>