Switch sigpending over to rt_sigpending.

Change-Id: I7b28984796b5fb343cfbcc47e0afc3a84293d417
diff --git a/libc/Android.mk b/libc/Android.mk
index 88be78d..417d0ab 100644
--- a/libc/Android.mk
+++ b/libc/Android.mk
@@ -246,6 +246,7 @@
     bionic/seteuid.cpp \
     bionic/setlocale.cpp \
     bionic/signalfd.cpp \
+    bionic/sigpending.cpp \
     bionic/sigprocmask.cpp \
     bionic/sigsuspend.cpp \
     bionic/sigwait.cpp \