Wrong order of include directories when build from SeaHorn

[agurfinkel]

When crab-llvm is include in SeaHorn as a sub-project it looks first inside the installed include directories as opposed to its source location. Every time the headers change, the build fails because it finds the old header files first.

Current work-around is to delete BUILD_DIR/crab_llvm and BUILD_DIR/crab manually.

It would be more convenient if the order of include directories is fixed.

[caballa]

@agurfinkel seems to fix the problem here 2977041.
I close it for now.