crazy linker: Fix RELRO sharing with packed relocations.

crazy linker: Fix RELRO sharing with packed relocations.

Packed relative relocations do not currently participate in
relocation of shared RELRO pages into a service process's load
addresses.  This undermines RELRO sharing, by reducing the
number of swapped RELRO pages (often to zero).

Fix by processing packed relative relocations a second time when
relocating shared RELRO pages.  Also, tidy up and rationalize
some duplicated code through use of templates.

BUG=385553
Committed: https://crrev.com/733a3f04a20043a7afb55c1a25d14dbaf869b913
Cr-Commit-Position: refs/heads/master@{#326773}

[simonb (inactive), 2015-04-22 12:52:46]

simonb@chromium.org changed reviewers:
+ rmcilroy@chromium.org, simonb@chromium.org

[rmcilroy, 2015-04-22 15:46:15]

lgtm, thanks.

[simonb (inactive), 2015-04-24 11:32:52]

The CQ bit was checked by simonb@chromium.org

[simonb (inactive), 2015-04-24 11:32:53]

The patchset sent to the CQ was uploaded after l-g-t-m from
rmcilroy@chromium.org
Link to the patchset: https://codereview.chromium.org/1099253002/#ps20001
(title: "Rebase to master.")

[commit-bot: I haz the power, 2015-04-24 11:32:58]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1099253002/20001

[commit-bot: I haz the power, 2015-04-24 11:55:55]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-04-24 11:56:50]

Patchset 2 (id:??) landed as
https://crrev.com/733a3f04a20043a7afb55c1a25d14dbaf869b913
Cr-Commit-Position: refs/heads/master@{#326773}