Stop googletest in subprojects

[ruairimoran]

Problem

• In the example folder, the cmake file fetches GPUtils.
• This causes a further fetch of googletest.
• Then googletest slows down the building process of the example project.
• We need to prevent gtest either from getting into the fetch or from being built by the example project.

Current solution

Make a release branch, and comment out the second part of the root CMakeLists.txt file

Proper solution

Use flags to default=OFF the debug parts of CMakeLists.txt file:

if(NOT GPUTILS_BUILD_TESTING)
    set(GPUTILS_BUILD_TESTING OFF)
endif()
if (GPUTILS_BUILD_TESTING)
    add_subdirectory(tests)
endif()
unset(GPUTILS_BUILD_TESTING CACHE)

Then, when building, pass the flag setting you want. For example, in the ci script

cmake -S . -B ./build -Wno-dev -DGPUTILS_BUILD_TESTING=ON