Fix multiple rules generating icudtl.dat

Fix multiple rules generating icudtl.dat

The icudata target is built for multiple toolsets, but the outputs of
the copies action are toolset-independent. Gyp then generates two
different ninja rules to do the same copies action.

To fix this, extract the copying of icudtl.dat to its own target that
supports only a single toolset (so nobody accidentally depends on the
wrong one) and then explicitly depend on that target+toolset from the
icudata target.

BUG=351052

[cjhopman, 2014-06-06 20:59:09]

mark: *

[cjhopman, 2014-06-06 21:07:19]

+a couple people to cc as fyi

[Mark Mentovai, 2014-06-06 21:10:03]

Jungshik should do the review (but LGTM if he approves it).

[jungshik at Google, 2014-06-10 00:26:00]

Thank you for doing this and sorry that I didn't get back to this much sooner. 
LGTM

[jungshik at Google, 2014-06-10 00:26:28]

On 2014/06/10 00:26:00, Jungshik Shin wrote:
> Thank you for doing this and sorry that I didn't get back to this much sooner.

> LGTM

[jungshik at Google, 2014-06-10 17:07:20]

On 2014/06/10 00:26:00, Jungshik Shin wrote:
> Thank you for doing this and sorry that I didn't get back to this much sooner.

> LGTM

I took this CL to apply to ICU 52, which will be rolled into the ToT (asas I got
the approval). For icu46 (used by M35-36), this CL will be still necessary if we
need to keep the build process saner in branches.