Fix clang tooling build on Linux (shim CMake in LLVM tree).

Fix Clang tooling build on Linux.

Since the chrome clang tools are built outside the LLVM tree, direct
references to LLVM/Clang libraries don't work as expected on Linux.
This patch changes the Clang update script to create a shim directory
for triggering the Chrome tools build as part of the LLVM build. The
shim CMakeLists.txt just forwards to the real one in tools/clang. As
a bonus, this allows the CMake files in tools/clang to just use
CMAKE_SOURCE_DIR/CMAKE_BINARY_DIR instead of having to manually
specify the LLVM source/binary dirs. In addition, with this change,
it's possible to have incremental builds of tools, since the script
no longer blows away the output directory.

Committed: https://crrev.com/42d9711d127ddc3e192747ff0901c4c6c29b5eae
Cr-Commit-Position: refs/heads/master@{#298152}

[dcheng, 2014-10-02 00:09:00]

dcheng@chromium.org changed reviewers:
+ hans@chromium.org

[dcheng, 2014-10-02 01:02:50]

Here's my preferred approach. It just creates a shim CMakeLists.txt and allows
us to use more standard CMake variables. The tricky part is we need custom
install rules, since we'd like to be able to run install steps for the chromium
tools separately.

[hans, 2014-10-03 01:23:45]

Sorry for the delay. I agree this is probably the nicer approach.

Being more on the "inside" of the build system might also become handy when we
start thinking about Windows and want to link the plugins into the clang binary.

https://codereview.chromium.org/615083006/diff/20001/tools/clang/scripts/upda...
File tools/clang/scripts/update.sh (right):

https://codereview.chromium.org/615083006/diff/20001/tools/clang/scripts/upda...
tools/clang/scripts/update.sh:441:
CHROME_TOOLS_SHIM_DIR=${ABS_LLVM_DIR}/tools/chrometools
Why aren't we inserting the shim under tools/clang/tools/extra/ ? That's where I
thought it would be spontaneously.

[dcheng, 2014-10-03 03:47:51]

https://codereview.chromium.org/615083006/diff/20001/tools/clang/scripts/upda...
File tools/clang/scripts/update.sh (right):

https://codereview.chromium.org/615083006/diff/20001/tools/clang/scripts/upda...
tools/clang/scripts/update.sh:441:
CHROME_TOOLS_SHIM_DIR=${ABS_LLVM_DIR}/tools/chrometools
On 2014/10/03 01:23:45, hans wrote:
> Why aren't we inserting the shim under tools/clang/tools/extra/ ? That's where
I
> thought it would be spontaneously.

There's only one call to add_llvm_implicit_external_projects(), and it happens
in llvm/tools/CMakeLists.txt =/

[hans, 2014-10-03 17:07:14]

lgtm

https://codereview.chromium.org/615083006/diff/20001/tools/clang/scripts/upda...
File tools/clang/scripts/update.sh (right):

https://codereview.chromium.org/615083006/diff/20001/tools/clang/scripts/upda...
tools/clang/scripts/update.sh:441:
CHROME_TOOLS_SHIM_DIR=${ABS_LLVM_DIR}/tools/chrometools
On 2014/10/03 03:47:51, dcheng wrote:
> On 2014/10/03 01:23:45, hans wrote:
> > Why aren't we inserting the shim under tools/clang/tools/extra/ ? That's
where
> I
> > thought it would be spontaneously.
> 
> There's only one call to add_llvm_implicit_external_projects(), and it happens
> in llvm/tools/CMakeLists.txt =/

OK. Let's keep it here, then.

[dcheng, 2014-10-04 00:12:10]

The CQ bit was checked by dcheng@chromium.org

[dcheng, 2014-10-04 00:12:11]

I've tested that this works on Mac/Linux before/after this patch without
clobbering, so hopefully everything will Just Work (tm)...

[commit-bot: I haz the power, 2014-10-04 00:17:29]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/615083006/20001

[commit-bot: I haz the power, 2014-10-04 01:19:26]

Committed patchset #2 (id:20001) as 1fb765347d1ff2041bcecc1bca447e0fa04a26dd

[commit-bot: I haz the power, 2014-10-04 01:20:38]

Patchset 2 (id:??) landed as
https://crrev.com/42d9711d127ddc3e192747ff0901c4c6c29b5eae
Cr-Commit-Position: refs/heads/master@{#298152}