meson: Prepare for subprojects

Google-Bug-Id: 179721407
Change-Id: I517dcb47d7c73fa4f3c7fcc25146b77de50d69b8
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/.gitignore b/.gitignore
index 1eab063..499916c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,3 @@
 /**/build*/
 /**/subprojects/*/
+/**/subprojects/*.wrap