meson: Use subprojects where possible

Change-Id: Id49b7db21f7f44d5183549430988fd33b9166edb
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/subprojects/googletest.wrap b/subprojects/googletest.wrap
new file mode 100644
index 0000000..56da9ef
--- /dev/null
+++ b/subprojects/googletest.wrap
@@ -0,0 +1,3 @@
+[wrap-git]
+url = https://github.com/google/googletest
+revision = HEAD