Set SA_RESTORER in sigaction()

GDB looks for specific opcode sequences when trying to recognize a stack
frame as a signal trampoline.  The sequences it looks for happen to be those
created when SA_RESTORER is set, since glibc always sets a restorer.  This
patch does the same here, so that the trampolines can be correctly identified.

Change-Id: I0ac574a68818cb24d939c3527f3aaeb04b853d04
diff --git a/libc/Android.mk b/libc/Android.mk
index f627640..8dd124e 100644
--- a/libc/Android.mk
+++ b/libc/Android.mk
@@ -295,6 +295,8 @@
 	arch-arm/bionic/sigsetjmp.S \
 	arch-arm/bionic/strlen.c.arm \
 	arch-arm/bionic/syscall.S \
+	arch-arm/bionic/sigaction.c \
+	arch-arm/bionic/__sig_restorer.S \
 	string/memmove.c.arm \
 	string/bcopy.c \
 	string/strcmp.c \