Use clang as default host compiler when cross-compiling

Use clang as default host compiler when cross-compiling

chrome/android still used system gcc as host compiler, and system gcc is
gcc 4.6 on Ubuntu Precise. This is too old.

Instead, use clang by default as host compiler (except when building for
AOSP, see http://crbug.com/377684 for that). This is controlled by a new
gyp variable host_clang, which only has an effect if clang=0. The existing
clang gyp variable means "use clang for everything"; if it's not set then
host_clang means "use clang for host compiles".

If your system gcc is 4.8+ and you don't want to use clang, you can set
host_clang=0 to use system gcc for host compiles instead.

In host_clang mode, our clang plugins currently aren't used (I figure if you
want plugins, you can just use clang=1). clang_warning_flags on the other
hand are used, to make sure the build stays warning-free.

BUG=360311
R=hans@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=287386

[hans, 2014-08-04 16:57:58]

lgtm, Nice!

> Use clang as default host compiler when cross-compiling
> 
> chrome/android still used system gcc as host compiler, and system gcc is
> gcc 4.6 on Ubuntu Precise. This is too old.

Maybe mention that this is in the context of switching Linux builds to Clang by
default, otherwise it may not be clear what "still used system gcc as host
compiler" refers to.

https://codereview.chromium.org/430383002/diff/140001/build/common.gypi
File build/common.gypi (right):

https://codereview.chromium.org/430383002/diff/140001/build/common.gypi#newco...
build/common.gypi:613: # compiler. Always do this by default, except when
building for AOSP.
Maybe include a link to the AOSP related crbug here?

[Nico, 2014-08-04 17:26:40]

On 2014/08/04 16:57:58, hans wrote:
> lgtm, Nice!
> 
> > Use clang as default host compiler when cross-compiling
> > 
> > chrome/android still used system gcc as host compiler, and system gcc is
> > gcc 4.6 on Ubuntu Precise. This is too old.
> 
> Maybe mention that this is in the context of switching Linux builds to Clang
by
> default, otherwise it may not be clear what "still used system gcc as host
> compiler" refers to.

I think it's clear from the BUG link (and if not, now from the codereview link).


> https://codereview.chromium.org/430383002/diff/140001/build/common.gypi
> File build/common.gypi (right):
> 
>
https://codereview.chromium.org/430383002/diff/140001/build/common.gypi#newco...
> build/common.gypi:613: # compiler. Always do this by default, except when
> building for AOSP.
> Maybe include a link to the AOSP related crbug here?

Done.

[Nico, 2014-08-04 17:44:38]

The CQ bit was checked by thakis@chromium.org

[commit-bot: I haz the power, 2014-08-04 17:46:26]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/thakis@chromium.org/430383002/160001

[Nico, 2014-08-04 19:05:24]

Committed patchset #9 manually as r287386 (presubmit successful).