Turn BUILD_TESTING off if EXECUTORCH_BUILD_TESTS is off

As the comment notes, it looks like otherwise we have third-party deps that might include(CTest) and thereby turn on testing even though our specific option is off. (Should we get rid of the specific option or more directly alias it to BUILD_TESTING?)


ghstack-source-id: 50971cb
ghstack-comment-id: 3081826265
Pull-Request: #12566

Author: swolchok

CMakeLists.txt

@@ -165,6 +165,10 @@ endif()
 
 if(EXECUTORCH_BUILD_TESTS)
   include(CTest)
+else()
+  # It looks like some of our third-party deps will try to turn this
+  # on if it's not explicitly set, leading to confusing behavior.
+  set(BUILD_TESTING OFF)
 endif()
 
 add_subdirectory(third-party)