Fix libc++ ARM build

Fix libc++ ARM build

libc++abi has a dependency on libunwind (only on ARM builds), so this
CL adds a new DEPS entry for libunwind and wires the necessary
machinery to fix the ARM build.

BUG=735133
R=thakis@chromium.org

Committed: 8921af0a0c50afd7988eab9efa3d0987a213b25f

[Tom Anderson, 2017-06-20 19:33:31]

Description was changed from

==========
Fix libc++ ARM build

BUG=735133
==========

to

==========
Fix libc++ ARM build

libc++abi has a dependency on libunwind (only on ARM builds), so this
CL adds a new DEPS entry for libunwind and wires the necessary
machinery to fix the ARM build.

BUG=735133
R=thakis@chromium.org
==========

[Tom Anderson, 2017-06-20 19:33:43]

thomasanderson@chromium.org changed reviewers:
+ thakis@chromium.org

[Tom Anderson, 2017-06-20 19:33:43]

thakis ptal

[Nico, 2017-06-20 19:37:09]

Cool!

Generally lgtm

One thing I'm wondering about: Once this libc++/linux project is done, I'd love
to use the same mechanism for libc++ on android (instead of using libc++ from
the NDK, like we currently do). Do you happen to know how the unwind situation
looks on android? Looks like we link against system libunwind there:
https://cs.chromium.org/chromium/src/build/config/android/BUILD.gn?type=cs&q=...

So maybe you could add is_linux to the target_os == "arm" conditional.

https://codereview.chromium.org/2946073002/diff/1/third_party/libunwind/OWNERS
File third_party/libunwind/OWNERS (right):

https://codereview.chromium.org/2946073002/diff/1/third_party/libunwind/OWNER...
third_party/libunwind/OWNERS:1: # You may only be an owner of libunwind if your
username begins with 'th'.
:-)

[Tom Anderson, 2017-06-20 19:45:04]

On 2017/06/20 19:37:09, Nico wrote:
> Cool!
> 
> Generally lgtm
> 
> One thing I'm wondering about: Once this libc++/linux project is done, I'd
love
> to use the same mechanism for libc++ on android (instead of using libc++ from
> the NDK, like we currently do). Do you happen to know how the unwind situation
> looks on android? Looks like we link against system libunwind there:
>
https://cs.chromium.org/chromium/src/build/config/android/BUILD.gn?type=cs&q=...
> 
> So maybe you could add is_linux to the target_os == "arm" conditional.

Done.

We might need to remove it later though, since the libunwind *needs* to be the
llvm impl.  But this may be ok already if we already use that impl on Android.

> https://codereview.chromium.org/2946073002/diff/1/third_party/libunwind/OWNERS
> File third_party/libunwind/OWNERS (right):
> 
>
https://codereview.chromium.org/2946073002/diff/1/third_party/libunwind/OWNER...
> third_party/libunwind/OWNERS:1: # You may only be an owner of libunwind if
your
> username begins with 'th'.
> :-)

[Tom Anderson, 2017-06-20 19:45:51]

Description was changed from

==========
Fix libc++ ARM build

libc++abi has a dependency on libunwind (only on ARM builds), so this
CL adds a new DEPS entry for libunwind and wires the necessary
machinery to fix the ARM build.

BUG=735133
R=thakis@chromium.org
==========

to

==========
Fix libc++ ARM build

libc++abi has a dependency on libunwind (only on ARM builds), so this
CL adds a new DEPS entry for libunwind and wires the necessary
machinery to fix the ARM build.

BUG=735133
R=thakis@chromium.org

Committed: 8921af0a0c50afd7988eab9efa3d0987a213b25f
==========

[Tom Anderson, 2017-06-20 19:45:53]

Committed patchset #2 (id:20001) manually as
8921af0a0c50afd7988eab9efa3d0987a213b25f (presubmit successful).