Clean up sys_signame and sys_siglist a little.

We don't need quite so much duplication because we already have a way
to get the signal number from its name, and that already copes with the
fact that the mips/mips64 numbers are different from everyone else's.

Also remove sys_signame from LP64. glibc doesn't have this BSD-ism.

Change-Id: I6dc411a3d73589383c85d3b07d9d648311492a10
diff --git a/libc/bionic/strerror_r.cpp b/libc/bionic/strerror_r.cpp
index 81120ec..5f2d362 100644
--- a/libc/bionic/strerror_r.cpp
+++ b/libc/bionic/strerror_r.cpp
@@ -34,7 +34,7 @@
 }
 
 static const Pair _sys_signal_strings[] = {
-#define  __BIONIC_SIGDEF(x,y,z)  { y, z },
+#define  __BIONIC_SIGDEF(signal_number, signal_description)  { signal_number, signal_description },
 #include <sys/_sigdefs.h>
   { 0, NULL }
 };