Now that the runtime fetches the true physical page size from the OS,
make the physical page size used by heap growth a variable instead of
a constant. This isn't used in any performance-critical paths, so it
shouldn't be an issue.

sys.PhysPageSize is also renamed to sys.DefaultPhysPageSize to make it
clear that it's not necessarily the true page size. There are no uses
of this constant any more, but we'll keep it around for now.

Updates #12480 and #10180.

Change-Id: I6c23b9df860db309c38c8287a703c53817754f03
Reviewed-on: https://go-review.googlesource.com/25022
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>

After mdempsky's recent changes, these are the only references to
"TheChar" left in the Go tree. Without the context, and without
knowing the history, this is confusing.

Also rename sys.TheGoos and sys.TheGoarch to sys.GOOS
and sys.GOARCH.

Also change the heap dump format to include sys.GOARCH
rather than TheChar, which is no longer a concept.

Updates #15169 (changes heapdump format)

Change-Id: I3e99eeeae00ed55d7d01e6ed503d958c6e931dca
Reviewed-on: https://go-review.googlesource.com/21647
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

Apparently its last use was removed in CL 8899.

Change-Id: I4f3a789b3cc4c249582e81463af62b576a281e40
Reviewed-on: https://go-review.googlesource.com/16880
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Minux Ma <minux@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

runtime/internal/sys will hold system-, architecture- and config-
specific constants.

Updates #11647

Change-Id: I6db29c312556087a42e8d2bdd9af40d157c56b54
Reviewed-on: https://go-review.googlesource.com/16817
Reviewed-by: Russ Cox <rsc@golang.org>