With this update, we now use our custom `serenity` Clang target, which
means that all system-specific compilation options (e.g. default PIE,
header search paths) will be handled automatically.
This port has been tested to build `Source/little` on all 4
toolchain-architecture pairs. Furthermore, `lib(std)c++` headers are
picked up correctly and our AK headers can be included without any
issues.
Due to recent kernel fixes related to memory-mapped files, the LLD
linker can now be used by default, so there's no need to also build the
GCC port alongside this.
Although our patches cover building libLLVM as a shared library, this is
currently not enabled by default, as DynamicLoader is very slow in
dealing with such a large number of relocations.
