Added a case to build_config.h to cover compiling for Linux with 16-bit wchar...

Added a case to build_config.h to cover compiling for Linux with 16-bit wchars
(alongside the existing cases for Windows with 16-bit wchars and Linux with
32-bit wchars) so that it becomes possible to compile and link the Chromium
base together with third-party libraries that require short wchars.

BUG=none
TEST=none

[Matthew Steele, 2009-10-21 19:18:00]

A small addition to build_config.h to make it possible to build on Linux with
16-bit wchars.

[tony, 2009-10-21 20:22:16]

FWIW, I think this is a bad idea.  Is it possible to recompile the third party
libs without -fshort-wchar or are they existing shared objects that you're
loading?

[Mark Mentovai, 2009-10-21 20:24:39]

Wow, bad.

This will put us in a really bad situation: we'll work with the third-party
libraries that require -fshort-wchar, but we won't work with the larger number
of native libraries that don't require it.

I'm specifically thinking about the interface to libstdc++.  We really don't
want to break that.

[brettw, 2009-10-21 22:29:27]

This is for another team using base, not changing the Chrome build.

The other team is in charge of their own build, what __WCHAR_MAX__ is set to for
their build,  and making sure all of their libraries work with it.

Is there any problem with this in Chrome-base land? The worst I could think of
is that there are possibly some uses of #ifdef OS_WIN that are used to trigger
16- vs 32-bit decisions, that will need to be updated to use the WCHAR_T_IS...
macros. I think this makes sense to do for base (if we had to do this for all of
Chrome, I would be more concerned).

[Mark Mentovai, 2009-10-21 22:39:20]

LGTM in that case.  My fear is that someone will find this and try to build
Chromium with -fshort-wchar.  Maybe we should put a big scary comment there
saying "warranty void except where prohibited by law."

[brettw, 2009-10-22 18:04:46]

Checked in as r29786. I added a warning that this mode isn't necessarily
supported for all projects.