Fix libdl dependency on Android and remove librt hack.

Fix libdl dependency on Android and remove librt hack.

The libdl library is already included on target builds of Android and needs
to be added to the build command line with a particular order to avoid
undefined references in other libraries. Fix this by only explicitly including
it in host builds and relying on the implicit inclusion on target builds.

Also remove the librt hack which is not longer necessary due to the AOSP build
bot having been removed.

BUG=chromium:469973
LOG=Y

Committed: https://crrev.com/11c4e2f2f7fe4f355b0e608b3a0babc2def48782
Cr-Commit-Position: refs/heads/master@{#27535}

[rmcilroy, 2015-03-31 11:23:13]

rmcilroy@chromium.org changed reviewers:
+ bmeurer@chromium.org, jarin@chromium.org, jochen@chromium.org

[rmcilroy, 2015-03-31 11:23:14]

jochen for libdl fix
bmeurer for librt hack removal 
jarin as FYI for perf-jit comment removal.

PTAL, thanks!

[rmcilroy, 2015-03-31 11:24:02]

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

[commit-bot: I haz the power, 2015-03-31 11:24:18]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1036133005/1

[commit-bot: I haz the power, 2015-03-31 11:28:31]

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

[commit-bot: I haz the power, 2015-03-31 11:28:33]

Try jobs failed on following builders:
  v8_presubmit on tryserver.v8 (JOB_FAILED,
http://build.chromium.org/p/tryserver.v8/builders/v8_presubmit/builds/1638)

[jochen (gone - plz use gerrit), 2015-03-31 11:31:25]

lgtm

[Jarin, 2015-03-31 11:43:17]

looks great. thanks.

[rmcilroy, 2015-03-31 12:00:40]

The CQ bit was checked by rmcilroy@chromium.org

[commit-bot: I haz the power, 2015-03-31 12:00:58]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1036133005/1

[commit-bot: I haz the power, 2015-03-31 12:08:17]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-31 12:08:33]

Patchset 1 (id:??) landed as
https://crrev.com/11c4e2f2f7fe4f355b0e608b3a0babc2def48782
Cr-Commit-Position: refs/heads/master@{#27535}