Add YOGA_ROOTS to permit multiple definitions

Summary:
This changes the `YOGA_ROOT` to `YOGA_ROOTS` in `YOGA_DEFS`. This allows the
inclusion of Yoga in the exported Components libraries directory and
back-references to the nested dependencies within it.

Reviewed By: rspencer01

Differential Revision: D4721745

fbshipit-source-id: 2dc9d4a730076510aed02027cb6713f6326c588d

lib/gtest/BUCK

@@ -22,6 +22,6 @@ cxx_library(
         ("googletest/googletest", "src/*.cc"),
     ]),
     header_namespace = "",
-    visibility = [YOGA_ROOT],
+    visibility = YOGA_ROOTS,
     deps = [],
 )