Fix WebP linking if CMAKE_FIND_PACKAGE_PREFER_CONFIG is ON

[bebuch]

Description

I use CMake with CMAKE_FIND_PACKAGE_PREFER_CONFIG. WebP installs its own config files which but doesn't respect CMAKE_DEBUG_POSTFIX in WEBP_LIBRARIES. Linking to the target resolves that issue.

Tests

It would be usefull to add a test pipline where CMake is called with CMAKE_FIND_PACKAGE_PREFER_CONFIG. However this is out of scope to this PR and should be done by a separate patch. Unfortunately, I don't currently have the time to familiarize myself enough to do this myself.

Checklist:

• I have read the contribution guidelines.
• (not applicable) If this is more extensive than a small change to existing code, I
  have previously submitted a Contributor License Agreement
  (individual, and if there is any way my
  employers might think my programming belongs to them, then also
  corporate).
• (not applicable) I have updated the documentation, if applicable.
• (not applicable) I have ensured that the change is tested somewhere in the testsuite
  (adding new test cases if necessary).
• My code follows the prevailing code style of this project.

[lgritz]

Actually, I think that the right solution is to edit our FindWebP.cmake, which tries to set those targets but gets the capitalization wrong, calling them WebP::WebP and WebP::WebPDemux.

If you fix our FindWebP.cmake to match the naming conventions of webp's own exported cmake configs, then in this spot, you can just replace ${WEP_LIBRARIES} with the targets, without needing the if at all.

What do you think?

[bebuch]

I updated the patch accordingly :-)

[lgritz]

@bebuch In the time since you first submitted this, we have switched to accepting all new code under Apache-2.0 license (changing from our historical use of BSD-3-Clause) and also enabled use of DCO sign-off.

Would you mind please acknowledging here (a comment in this PR is sufficient) that you are ok submitting under Apache-2.0?

And also, could you please do the sign-off so it passes the DCO check? The easiest way to do that is:

git commit --amend -s             # the -s will add the sign-off line
git push origin patch-2 --force

[bebuch]

I'm fine with submitting under Apache-2.0 license.