Sort and fix `#include` directives.

Includes are sorted into groups, each sorted alphabetically and separated by a
blank line. The groups are, in order, C headers, C++ headers, VIXL (non-backend)
headers, and VIXL backend headers.

Change-Id: I9a71430bffeaf77389a089487ce264db8d1d9ddc
diff --git a/test/test-invalset.cc b/test/test-invalset.cc
index 749ddcc..4985fbf 100644
--- a/test/test-invalset.cc
+++ b/test/test-invalset.cc
@@ -24,9 +24,8 @@
 // OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-#include "test-runner.h"
-
 #include "invalset-vixl.h"
+#include "test-runner.h"
 
 namespace vixl {