meson: add graphene subproject

So we can build all the OpenGL elements.

diff --git a/subprojects/graphene.wrap b/subprojects/graphene.wrap
new file mode 100644 (file)
index 0000000..1f61aec
--- /dev/null
+++ b/subprojects/graphene.wrap
@@ -0,0 +1,4 @@
+[wrap-git]
+directory=graphene
+url=https://github.com/ebassi/graphene.git
+revision=master
\ No newline at end of file