Restore sys_signame for LP64.

mksh is using this, and we probably build as much BSD source as glibc source.

Change-Id: I400d255a67f9614ca9e57090e3a2e49d2b10cba4
diff --git a/tests/signal_test.cpp b/tests/signal_test.cpp
index ea3096a..6d55bef 100644
--- a/tests/signal_test.cpp
+++ b/tests/signal_test.cpp
@@ -240,7 +240,7 @@
 }
 
 TEST(signal, sys_signame) {
-#if defined(__BIONIC__) && !defined(__LP64__)
+#if defined(__BIONIC__)
   ASSERT_TRUE(sys_signame[0] == NULL);
   ASSERT_STREQ("HUP", sys_signame[SIGHUP]);
 #else