gitignore: Add meson build directories

Change-Id: I6e480c6f561bba0fb3f654f89d78f21988aca3ba
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/.gitignore b/.gitignore
index 025c6c9..327ea97 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
+/build*/
 /subprojects/*/