meson: Don't build tests or examples if subproject

This can still be overridden, but it is probably the most sane setting.

Change-Id: I8aa4a68f94e536320d6203c2027119dc5d133984
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/meson.build b/meson.build
index e7c30b1..4f7bc49 100644
--- a/meson.build
+++ b/meson.build
@@ -3,7 +3,9 @@
         default_options: [
           'warning_level=3',
           'werror=true',
-          'cpp_std=c++17'
+          'cpp_std=c++17',
+          'tests=' + (meson.is_subproject() ? 'disabled' : 'auto'),
+          'examples=' + (meson.is_subproject() ? 'false' : 'true'),
         ])
 
 subdir('src')