str/cat: Rename from util/string

This still maintains backwards compatability.

Change-Id: Id984a9c2067aaa6986f892c1870834d77b8aec80
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/include/meson.build b/include/meson.build
index 83b536c..dc4de82 100644
--- a/include/meson.build
+++ b/include/meson.build
@@ -9,6 +9,7 @@
   'stdplus/pinned.hpp',
   'stdplus/raw.hpp',
   'stdplus/signal.hpp',
+  'stdplus/str/cat.hpp',
   'stdplus/util/cexec.hpp',
   'stdplus/util/string.hpp',
   'stdplus/zstring.hpp',