Don't export new/delete from libc shared libraries.

This used to be handled by -fvisibility=hidden on libc_cxa, but that
was broken by the resolution of https://llvm.org/PR22419 (introduced
to Android in today's clang update).

Now we just use a version script that prevents these from being
re-exported from our shared libraries.

Change-Id: Ib290e1d0d7426e09ad17a91178162fff6dbdcfa9
diff --git a/libc/version_script.txt b/libc/version_script.txt
new file mode 100644
index 0000000..afc5e5c
--- /dev/null
+++ b/libc/version_script.txt
@@ -0,0 +1,12 @@
+LIBC {
+  local:
+    _ZSt7nothrow;
+    _ZdaPv;
+    _ZdaPvRKSt9nothrow_t;
+    _ZdlPv;
+    _ZdlPvRKSt9nothrow_t;
+    _Znaj;
+    _ZnajRKSt9nothrow_t;
+    _Znwj;
+    _ZnwjRKSt9nothrow_t;
+};