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: Iae16aecd192c3c1dd388bd870d048c9ed3f63e98
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/test/meson.build b/test/meson.build
index 2025c64..d740b44 100644
--- a/test/meson.build
+++ b/test/meson.build
@@ -15,7 +15,7 @@
         )
         gmock_dep = gtest_proj.dependency('gmock')
     else
-        assert(not get_option('tests').enabled(),
+        assert(not get_option('tests').allowed(),
                'Googletest is required if tests are enabled')
     endif
 endif