build: Factorize dependency declarations for foo-make targets.

Signed-off-by: Diego Biurrun <diego@biurrun.de>
build: Replace stamps-based build of native clang with a direct file target.

Signed-off-by: Diego Biurrun <diego@biurrun.de>
build: Do not have configure targets depend on each other.

The real dependency is between the build targets, the configure
targets are just an implementation detail of the build targets.

Signed-off-by: Diego Biurrun <diego@biurrun.de>
build: Do not let configure targets depend on build targets.

Otherwise the configure targets are always run as their stamps are
older than the compile targets' stamps, which in turn triggers
spurious rebuilds.

Ensuring proper dependencies between the compile targets should be
sufficient to have everything build and rebuild in the correct order.

Signed-off-by: Diego Biurrun <diego@biurrun.de>
build: Resolve symlinks when determining S2E source directory location.

This allows using a symlink to the S2E Makefile in the build directory.

Signed-off-by: Diego Biurrun <diego@biurrun.de>
build: Remove guest tools build stamp after running guestclean.

This will trigger rebuilds of the guest tools after cleaning them.

Signed-off-by: Diego Biurrun <diego@biurrun.de>