android-x86: add sigsetjmp.S

It adds two functions sigsetjmp and siglongjmp
that fix compiling errors in bluetooth and mksh.

Copy directly from sigsetjmp.S of OpenBSD.

Change-Id: I4696f82ee6f85d1c93cbdd3c9e40f4917d50f3a6
diff --git a/libc/Android.mk b/libc/Android.mk
index 1981d0b..351ad02 100644
--- a/libc/Android.mk
+++ b/libc/Android.mk
@@ -393,6 +393,7 @@
 	arch-x86/bionic/_exit_with_stack_teardown.S \
 	arch-x86/bionic/setjmp.S \
 	arch-x86/bionic/_setjmp.S \
+	arch-x86/bionic/sigsetjmp.S \
 	arch-x86/bionic/vfork.S \
 	arch-x86/bionic/syscall.S \
 	arch-x86/string/bcopy_wrapper.S \