Add support for QNX Neutrino.

Add support for QNX Neutrino. 

This patch incorporates a change to source/common/putil.c 
fetched from upstream. 

In addition, it undefines 'si_value' in source/common/ucnvmbcs.c to 
avoid a collision with 'si_value' defined on some platforms.

Patch by: 
 Eli Fidler <efidler@blackberry.com>;, 
 Jeff Rogers <jrogers@blackberry.com>;, 
 Cosmin Truta <ctruta@blackberry.com>;.

The original CL is at https://codereview.chromium.org/141063008/

README.chromium was slightly updated to refer to the upstream change for
si_value.

TBR=mark@chromium.org
BUG=NONE 
TEST=icu is built properly on qnx. After DEPS roll, net_unittests:*IDN* and base_unittests:*String* all pass on qnx.

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=257503

[jungshik at Google, 2014-03-17 21:59:43]

Committed patchset #3 manually as r257503 (presubmit successful).

[Mark Mentovai, 2014-03-18 15:37:16]

https://codereview.chromium.org/195973005/diff/40001/icu.gyp
File icu.gyp (right):

https://codereview.chromium.org/195973005/diff/40001/icu.gyp#newcode136
icu.gyp:136: '_toolset != "host" or host_os != "mac")', {
No tabs.

https://codereview.chromium.org/195973005/diff/40001/source/common/unicode/pt...
File source/common/unicode/ptypes.h (right):

https://codereview.chromium.org/195973005/diff/40001/source/common/unicode/pt...
source/common/unicode/ptypes.h:38: #   include "unicode/pqnx.h"
I don’t see this file in this change.

[jungshik at Google, 2014-03-18 18:28:52]

On 2014/03/18 15:37:16, Mark Mentovai wrote:
> https://codereview.chromium.org/195973005/diff/40001/icu.gyp
> File icu.gyp (right):
> 
> https://codereview.chromium.org/195973005/diff/40001/icu.gyp#newcode136
> icu.gyp:136: '_toolset != "host" or host_os != "mac")', {
> No tabs.
> 
>
https://codereview.chromium.org/195973005/diff/40001/source/common/unicode/pt...
> File source/common/unicode/ptypes.h (right):
> 
>
https://codereview.chromium.org/195973005/diff/40001/source/common/unicode/pt...
> source/common/unicode/ptypes.h:38: #   include "unicode/pqnx.h"
> I don’t see this file in this change.

Ooops. Thanks a lot for catching these. (I haven't rolled DEPS, yet,
fortunately). A new CL to address them is at 
https://codereview.chromium.org/203823003