Export the INCLUDES DESTINATION without appending to the
INTERFACE_INCLUDE_DIRECTORIES of the target itself. That way, a target
can be exported multiple times with different INCLUDES DESTINATION
without unintended cross-pollution of export sets.
Make a C executable instead of attempting to make a C++ static
library (and not really succeeding). This was introduced in
commit 894f52f3 (Handle INTERFACE properties transitively for
includes and defines., 2012-09-23).