meson: Make googletest vendorable

This is a quality of life improvement so that users trying to work with
the project don't need to have an external install of the googletest
dependency for the tests to build.

Change-Id: I44b4cbae14c5006eaef0a5b42a1f6b753b07b405
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..025c6c9
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+/subprojects/*/