Changes to allow for support on macOS

What

This MR makes a few changes and fixes to allow for compiling on macOS.

All checks are done on my laptop, running macOS Catalina v10.15.7. The changes should not really depend on the explicit macOS, however.

Remove Linux-specific sources from the build

The main change is to the CMakeLists.txt file in libDevCom. There a new list of sources are created which contain the source for devices that depend explicitly on Linux drivers. If, during the CMake configuration step it is detected that we are on macOS, those sources are not included in the build.

The current sources that are found to depend explicitly on Linux device drivers are: SPIDevCom and I2CDevCom.

Fix the check for Clang

Updates the check for Clang version by using the MATCHES requirement instead of the STREQUAL requirement in src/CMakeLists.txt:

if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")

becomes

if ("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang")

Miscellaneous

Change CMake message outputs from message(...) to message(STATUS...)