Fix finding gtest and gmock in cmake.

[hgaiser]

This PR is to update how GTest and GMock are found using CMake. The old way has issues with system installed versions of these packages (see here).

[lprobsth]

This patch fixes an error when building ros-noetic-catkin on arch linux with cmake version 3.30.2.

Log from makepkg

==> Making package: ros-noetic-catkin 0.8.10-3 (Mi 28 Aug 2024 22:54:12 CEST)
==> Checking runtime dependencies...
==> Checking buildtime dependencies...
==> Retrieving sources...
  -> Found ros-noetic-catkin-0.8.10.tar.gz
==> Validating source files with sha256sums...
    ros-noetic-catkin-0.8.10.tar.gz ... Passed
==> Extracting sources...
  -> Extracting ros-noetic-catkin-0.8.10.tar.gz with bsdtar
==> Removing existing $pkgdir/ directory...
==> Starting build()...
CMake Deprecation Warning at CMakeLists.txt:1 (cmake_minimum_required):
  Compatibility with CMake < 3.5 will be removed from a future version of
  CMake.

  Update the VERSION argument <min> value or use a ...<max> suffix to tell
  CMake that the project does not need compatibility with older versions.


-- Using CATKIN_DEVEL_PREFIX: /home/lprobsth/.cache/yay/ros-noetic-catkin/src/build/devel
-- Using CMAKE_PREFIX_PATH: /opt/ros/noetic
-- This workspace overlays: /opt/ros/noetic
CMake Warning (dev) at cmake/python.cmake:4 (find_package):
  Policy CMP0148 is not set: The FindPythonInterp and FindPythonLibs modules
  are removed.  Run "cmake --help-policy CMP0148" for policy details.  Use
  the cmake_policy command to set the policy and suppress this warning.

Call Stack (most recent call first):
  cmake/all.cmake:164 (include)
  CMakeLists.txt:8 (include)
This warning is for project developers.  Use -Wno-dev to suppress it.

-- Using PYTHON_EXECUTABLE: /usr/bin/python
-- Using default Python package layout
-- Using empy: /usr/lib/python3.12/site-packages/em.py
-- Using CATKIN_ENABLE_TESTING: ON
-- Call enable_testing()
-- Using CATKIN_TEST_RESULTS_DIR: /home/lprobsth/.cache/yay/ros-noetic-catkin/src/build/test_results
-- Forcing gtest/gmock from source, though one was otherwise available.
-- Found gtest sources under '/usr/src/gmock': gtests will be built
-- Found gmock sources under '/usr/src/gmock': gmock will be built
CMake Warning at /usr/src/gmock/CMakeLists.txt:40 (project):
  VERSION keyword not followed by a value or was followed by a value that
  expanded to nothing.


CMake Warning at /usr/src/googletest/CMakeLists.txt:50 (project):
  VERSION keyword not followed by a value or was followed by a value that
  expanded to nothing.


CMake Error at /usr/src/googletest/CMakeLists.txt:124 (set_target_properties):
  set_target_properties called with incorrect number of arguments.


CMake Error at /usr/src/googletest/CMakeLists.txt:142 (set_target_properties):
  set_target_properties called with incorrect number of arguments.


CMake Error at /usr/src/gmock/CMakeLists.txt:99 (set_target_properties):
  set_target_properties called with incorrect number of arguments.


CMake Error at /usr/src/gmock/CMakeLists.txt:102 (set_target_properties):
  set_target_properties called with incorrect number of arguments.


-- Using Python nosetests: /usr/bin/nosetests-3.12
-- catkin 0.8.10
-- BUILD_SHARED_LIBS is on
-- Configuring incomplete, errors occurred!
==> ERROR: A failure occurred in build().
    Aborting...