To speed up the `AUTOGEN` configuration process, evaluate the compiler
features only once. The feature evaluation result is stored in the new class
`cmQtAutoGen::CompilerFeatures`, and the instance is shared by using
`std::shared_ptr`.
The new `cmQtAutogenGlobalInitializer::Keywords` class instance is bound to
the lifetime of the `cmQtAutogenGlobalInitializer` instance. Global static
const strings would be allocated at program start and deallocated at program
end. Keeping keyword strings alive only in the context where they're
needed helps to reduce the memory footprint.
This adds the cmQtAutoGenGlobalInitializer::GetExecutableTestOutput method
which caches the output of the called executable and returns the cached value
on any subsequent call.
This teaches CMake the variables
- CMAKE_GLOBAL_AUTOGEN_TARGET
- CMAKE_GLOBAL_AUTOGEN_TARGET_NAME
- CMAKE_GLOBAL_AUTORCC_TARGET
- CMAKE_GLOBAL_AUTORCC_TARGET_NAME
which control the generation of global
``autogen`` and ``autorcc`` targets.
Closes#17721
