Add BUILD files for IMU board

Change-Id: I5437972c594ecd3ebeb24d9b9b96f2801b405021
Signed-off-by: James Kuszmaul <jabukuszmaul+collab@gmail.com>
diff --git a/tools/BUILD b/tools/BUILD
index 98e1348..cd98255 100644
--- a/tools/BUILD
+++ b/tools/BUILD
@@ -50,6 +50,11 @@
     constraint_values = ["@//tools/platforms/hardware:cortex_m0plus"],
 )
 
+config_setting(
+    name = "cpu_cortex-m4f-imu",
+    constraint_values = ["@//tools/platforms/hardware:cortex-m4f-imu"],
+)
+
 # TODO(phil): Re-enable this with proper support.
 #config_setting(
 #    name = "cpu_cortex_m4f_k22",