Add a wrapper for signalfd

The wrapper blocks (and unblock) signals for the thread as well.
This will get tested by the wakeup for the IPC.

Change-Id: Ica701034e8890fc0689b8528b4d7448fd630ed64
diff --git a/aos/ipc_lib/BUILD b/aos/ipc_lib/BUILD
index 03a4752..85f6dcd 100644
--- a/aos/ipc_lib/BUILD
+++ b/aos/ipc_lib/BUILD
@@ -148,3 +148,16 @@
         "@com_github_gflags_gflags//:gflags",
     ],
 )
+
+cc_library(
+    name = "signalfd",
+    srcs = [
+        "signalfd.cc",
+    ],
+    hdrs = [
+        "signalfd.h",
+    ],
+    deps = [
+        "//aos/logging",
+    ],
+)