.gitignore: add meson directories

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I6d96179a8e0b55a8c7e0d0c9c7c45e4f1f9562c5
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..de8712e
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+build*/
+subprojects/*/