link_directories and include_directories should not be called by toolchain

[redbaron]

According to this CMake issue when toolchain calls link_directories and include_directories these are detected as <LANG>_IMPLICIT_{LINK,INCLUDE}_DIRECTORIES and therefore removed from command line args.

Clearly your toolchain works in practice, but I suspect there could be cases where it can backfire. In the same issue CMake maintainers recommend using CMAKE_<LANG>_STANDARD_LIBRARIES and CMAKE_<LANG>_STANDARD_INCLUDE_DIRECTORIES by the toolchains.

[MarkSchofield]

Issue #67 called out that include_directories are bad, and I fixed those occurrences with #69. I'd love to replace link_directories but CMAKE_<LANG>_STANDARD_LINK_DIRECTORIES hasn't been implemented yet - it looks like it might be coming in CMake 3.31 - CMAKE__STANDARD_LINK_DIRECTORIES. When that's shipped I'd definitely like to move to it.