cmake/Findasio.cmake and cmake/Findcatch.cmake adapted for usage with…

[axelsommerfeldt]

… cross-compiling CMake toolchain files

Both files have been modified so they are able to find the git submodules 'dependency/asio' resp. 'dependency/catch' even if a CMake toolchain file was used with a different CMAKE_SYSROOT than / (which is common for cross-compiling CMake toolchain files).

See also: https://cmake.org/cmake/help/latest/variable/CMAKE_SYSROOT.html