Add BUILD files for IMU board

Change-Id: I5437972c594ecd3ebeb24d9b9b96f2801b405021
Signed-off-by: James Kuszmaul <jabukuszmaul+collab@gmail.com>
diff --git a/y2020/vision/sift/fast_gaussian.bzl b/y2020/vision/sift/fast_gaussian.bzl
index 1c29cdb..f0896cc 100644
--- a/y2020/vision/sift/fast_gaussian.bzl
+++ b/y2020/vision/sift/fast_gaussian.bzl
@@ -40,6 +40,7 @@
             "arm64": "aarch64",
             "cortex-m": "cortex-m",
             "cortex-m0plus": "cortex-m0plus",
+            "cortex-m4f-imu": "cortex-m4f-imu",
         }),
         outs = headers + objects + htmls,
         # The tool doesn't support everything right now.