fd: Add MMap handle object

This makes it possible to have an RAII managed MMap

Change-Id: Id61cea650a68087ca9d263a57dd780791845eb85
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/test/meson.build b/test/meson.build
index 7d26297..2634c45 100644
--- a/test/meson.build
+++ b/test/meson.build
@@ -45,6 +45,7 @@
     'fd/managed',
     'fd/intf',
     'fd/impl',
+    'fd/mmap',
     'fd/mock',
     'fd/ops',
   ]