Add pollset_set.h to build.json
diff --git a/BUILD b/BUILD
index 3acee96..6b9e554 100644
--- a/BUILD
+++ b/BUILD
@@ -171,6 +171,7 @@
     "src/core/iomgr/pollset.h",
     "src/core/iomgr/pollset_kick_posix.h",
     "src/core/iomgr/pollset_posix.h",
+    "src/core/iomgr/pollset_set.h",
     "src/core/iomgr/pollset_set_posix.h",
     "src/core/iomgr/pollset_set_windows.h",
     "src/core/iomgr/pollset_windows.h",
@@ -396,6 +397,7 @@
     "src/core/iomgr/pollset.h",
     "src/core/iomgr/pollset_kick_posix.h",
     "src/core/iomgr/pollset_posix.h",
+    "src/core/iomgr/pollset_set.h",
     "src/core/iomgr/pollset_set_posix.h",
     "src/core/iomgr/pollset_set_windows.h",
     "src/core/iomgr/pollset_windows.h",