Handled WPILib stupidly #defineing ERROR and get everything building.

Change-Id: Ie49be384cd4b2e2e9d26314a014eb21e158a6979
diff --git a/frc971/wpilib/hall_effect.h b/frc971/wpilib/hall_effect.h
index 407f2b9..d95b717 100644
--- a/frc971/wpilib/hall_effect.h
+++ b/frc971/wpilib/hall_effect.h
@@ -2,6 +2,7 @@
 #define FRC971_WPILIB_HALL_EFFECT_H_
 
 #include "DigitalInput.h"
+#undef ERROR
 
 namespace frc971 {
 namespace wpilib {