GN: Factor "stamp" and "copy" details out of toolchains

GN: Factor "stamp" and "copy" details out of toolchains

The "stamp" and "copy" tools are unlike all other tools in a toolchain:
their definitions are entirely generic to a given host operating system,
rather than depending on the exact the target of the toolchain.  Use the
same definitions in all toolchains, depending only on $host_os.

BUG=512869
R=dpranke@chromium.org

Committed: https://crrev.com/4d550a5990654c3dcfa9bbc38da3bbfa4e5c4796
Cr-Commit-Position: refs/heads/master@{#356416}

[Roland McGrath, 2015-10-27 21:22:39]

The CQ bit was checked by mcgrathr@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-10-27 21:24:05]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1412623007/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1412623007/1

[commit-bot: I haz the power, 2015-10-27 21:24:06]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-10-27 21:24:06]

Dry run: No L-G-T-M from a valid reviewer yet. Only full committers are
accepted.
Even if an L-G-T-M may have been provided, it was from a non-committer,
_not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[Dirk Pranke, 2015-10-27 21:40:55]

lgtm

[Roland McGrath, 2015-10-27 22:12:25]

The CQ bit was checked by mcgrathr@chromium.org

[commit-bot: I haz the power, 2015-10-27 22:13:21]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1412623007/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1412623007/1

[commit-bot: I haz the power, 2015-10-27 22:37:34]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-27 22:38:20]

Patchset 1 (id:??) landed as
https://crrev.com/4d550a5990654c3dcfa9bbc38da3bbfa4e5c4796
Cr-Commit-Position: refs/heads/master@{#356416}