build: use allowed over enabled

Meson feature options are typically in a tri-state of enabled, disabled,
or auto.  The enabled and disabled functions on an option (from
`get_option`) no longer return true for auto features.  Instead, the
expectation is to use `allowed()` which is true for both enabled and auto.

Switch all uses of `enabled` to `allowed`.

Change-Id: I0fe9c9363a6a6dc1cd508da03ab30dde022c5526
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/test/meson.build b/test/meson.build
index 0faf701..06267e9 100644
--- a/test/meson.build
+++ b/test/meson.build
@@ -16,7 +16,7 @@
       ])
     gmock = gtest_proj.dependency('gmock')
   else
-    assert(not get_option('tests').enabled(), 'Googletest is required')
+    assert(not get_option('tests').allowed(), 'Googletest is required')
   endif
 endif