FindPkgConfig: Fix TO_NATIVE_PATH escaping white spaces

White spaces in the environment variables should not be escaped
FindPkgConfig - Unit tests: Fix dummy pkg-config scripts
FindPkgConfig - Unit tests: Add quotes when setting CMAKE_PREFIX_PATH

This should fix when CMAKE_CURRENT_SOURCE_DIR contains a white space
Merge topic 'FindPkgConfig_Extend-PKG_CONFIG_PATH' into next

7ccae4dd FindPkgConfig - Unit tests: Add quotes when setting CMAKE_PREFIX_PATH
17f471d0 FindPkgConfig - Unit tests: Fix dummy pkg-config scripts
f92203ba FindPkgConfig: Fix TO_NATIVE_PATH escaping white spaces