[gflags]: Fix targets gflags::* not being globally visible

[JafarAbdi]

Describe the pull request

I'm getting the following error when calling find_package(gflags REQUIRED) in a cmake project

CMake Error at /home/jafar/workspaces/vcpkg/scripts/buildsystems/vcpkg.cmake:574 (_add_library):
  _add_library cannot create ALIAS target "gflags" because target
  "gflags::gflags" is imported but not globally visible.
Call Stack (most recent call first):
  /home/jafar/workspaces/vcpkg/installed/x64-linux/share/gflags/vcpkg-cmake-wrapper.cmake:7 (add_library)
  /home/jafar/workspaces/vcpkg/scripts/buildsystems/vcpkg.cmake:738 (include)
  CMakeLists.txt:4 (find_package)


CMake Error at /home/jafar/workspaces/vcpkg/scripts/buildsystems/vcpkg.cmake:574 (_add_library):
  _add_library cannot create ALIAS target "gflags_static" because target
  "gflags::gflags_static" is imported but not globally visible.
Call Stack (most recent call first):
  /home/jafar/workspaces/vcpkg/installed/x64-linux/share/gflags/vcpkg-cmake-wrapper.cmake:7 (add_library)
  /home/jafar/workspaces/vcpkg/scripts/buildsystems/vcpkg.cmake:738 (include)
  CMakeLists.txt:4 (find_package)


-- Configuring incomplete, errors occurred!
See also "/tmp/untitled/build/CMakeFiles/CMakeOutput.log".

after debugging it I think it happened after merging #18739 (I don't see the error when checking its parent commit), to fix it I used the solution described here

• Which triplets are supported/not supported? Have you updated the CI baseline?

  linux, No

• Does your PR follow the maintainer guide?

  Yes

• If you have added/updated a port: Have you run ./vcpkg x-add-version --all and committed the result?

  Yes

If you are still working on the PR, open it as a Draft: https://github.blog/2019-02-14-introducing-draft-pull-requests/

[Neumann-A]

Probably something like:

Suggested change

	set_target_properties("gflags::${tgt}" PROPERTIES IMPORTED_GLOBAL TRUE)
	add_library(${tgt} ALIAS "gflags::${tgt}")
	add_library(${tgt} INTERFACE IMPORTED UNKNOWN)
	target_link_libraries(${tgt} INTERFACE "gflags::${tgt}")

is better since it does not require to make the targets global.

[PhoebeHui]

@JafarAbdi, could you address the review suggestions?

[JafarAbdi]

@JafarAbdi, could you address the review suggestions?

Done, but I'm not sure why the CI is failing I also see the main branch is failing could that be related .?

[BillyONeal]

Done, but I'm not sure why the CI is failing I also see the main branch is failing could that be related .?

Yeah, sorry about that. We backed out the new check that caused a bunch of PRs to fail in the last 10 hours or so

[PhoebeHui]

Thanks for your updates!

[BillyONeal]

Thanks for the fix!