native-comp-available-p is the definitive test

* doc/lispref/compile.texi (Native Compilation): Document
native-comp-available-p as the way to test for native compilation.
* lisp/emacs-lisp/package.el (package--native-compile-async):
* test/lisp/mh-e/mh-utils-tests.el (mh-ensure-native-trampolines):
Test for native compilation with native-comp-available-p.

Thank you to Andrea Corallo for reviewing this patch.

doc/lispref/compile.texi

@@ -811,8 +811,7 @@ for you to be able to native-compile Lisp code.
 
 @vindex native-compile@r{, a Lisp feature}
   To determine whether the current Emacs process can produce and load
-natively-compiled Lisp code, test whether the @code{native-compile}
-feature is available (@pxref{Named Features}).  Alternatively, call
+natively-compiled Lisp code, call
 @code{native-comp-available-p} (@pxref{Native-Compilation Functions}).
 
   Unlike byte-compiled code, natively-compiled Lisp code is executed

lisp/emacs-lisp/package.el

@@ -1081,8 +1081,7 @@ This assumes that `pkg-desc' has already been activated with
   "Native compile installed package PKG-DESC asynchronously.
 This assumes that `pkg-desc' has already been activated with
 `package-activate-1'."
-  (when (and (featurep 'native-compile)
-             (native-comp-available-p))
+  (when (native-comp-available-p)
     (let ((warning-minimum-level :error))
       (native-compile-async (package-desc-dir pkg-desc) t))))
 

test/lisp/mh-e/mh-utils-tests.el

@@ -113,7 +113,7 @@ As `call-process'' and `file-directory-p' will be redefined, the
 native compiler will invoke `call-process' to compile the
 respective trampolines.  To avoid interferences with the
 `call-process' mocking we build these AOT."
-  (when (featurep 'native-compile)
+  (when (native-comp-available-p)
     (mapc #'comp-subr-trampoline-install '(call-process file-directory-p))))
 
 (defun mh-test-utils-setup-with-mocks ()