util/str: Add string concatentation methods

Change-Id: I5caf8e0731eb9ac0f18b84d25256ea0068fab03c
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/test/meson.build b/test/meson.build
index bcd016e..c8fddf0 100644
--- a/test/meson.build
+++ b/test/meson.build
@@ -6,6 +6,7 @@
   'handle/copyable',
   'handle/managed',
   'util/cexec',
+  'util/string',
 ]
 
 foreach t : tests