Avoid picking system-wide dependencies

[alexey-lysiuk]

Exclude any system-wide paths that may affect dependency lookup.

Mainly, it should be done for CMake based targets. Addition of knows paths to CMAKE_SYSTEM_IGNORE_PREFIX_PATH CMake variable (like /usr/local, Homebrew and MacPorts prefixes), and setting CMAKE_TOOLCHAIN_FILE environment variable to an empty string are the primary things to consider.