This CL is a roll-forward (tweaked slightly) of CL 467715, which
turned on text section splitting for GOARCH=arm. The intent is to
avoid recurrent problems with external linking where there is a
disagreement between the Go linker and the external linker over
whether a given branch will reach. In the past our approach has been
to tweak the reachability calculations slightly to try to work around
potential linker problems, but this hasn't proven to be very robust;
section splitting seems to offer a better long term fix.

Updates #58425.
Fixes #63317.

Change-Id: I7372d41abce84097906a3d0805b6b9c486f345d6
Reviewed-on: https://go-review.googlesource.com/c/go/+/531795
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
(cherry picked from commit 1e69040)
Reviewed-on: https://go-review.googlesource.com/c/go/+/532096
Auto-Submit: Dmitri Shuralyov <dmitshur@google.com>