meson: Use subprojects where possible

Change-Id: Id49b7db21f7f44d5183549430988fd33b9166edb
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..327ea97
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+/build*/
+/subprojects/*/