This makes it possible for projects to incorporate D-Bus as a CMake sub-project in a larger CMake project.
Before this PR, doing so would result in many errors.
This is because CMAKE_SOURCE_DIR and CMAKE_BINARY_DIR would point to directories above the D-Bus project.
Using paths relative to the project directory, PROJECT_SOURCE_DIR and PROJECT_BINARY_DIR, corrects for this.
[The libxml code path has been broken for at least 2.5 years, and Expat
is tiny, so there seems no point in supporting both. -smcv]
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=20253
Signed-off-by: Chengwei Yang <chengwei.yang@intel.com>
Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>