gnu: meson: Introduce versioned 'meson-0.60' variable.

While at it, change inheritance such that newest comes first.

* gnu/packages/build-tools.scm (meson-0.63): Move to the top.
(meson-0.60): Inherit from MESON-0.63.
(meson-0.59): Inherit from MESON-0.60.  Don't use PACKAGE/INHERIT.
(meson): Turn into alias for MESON-0.60.

gnu/packages/build-tools.scm

@@ -263,10 +263,10 @@ files and generates build instructions for the Ninja build system.")
       ;; X11 license.
       (license (list license:bsd-3 license:x11)))))
 
-(define-public meson
+(define-public meson-0.63
   (package
     (name "meson")
-    (version "0.60.3")
+    (version "0.63.2")
     (source (origin
               (method url-fetch)
               (uri (string-append "https://github.com/mesonbuild/meson/"
@@ -274,9 +274,7 @@ files and generates build instructions for the Ninja build system.")
                                   version ".tar.gz"))
               (sha256
                (base32
-                "13mrrizg4vl6n5k7fz6amyafnn3i097dcarr552qc0ca6nlmzjl7"))
-              (patches (search-patches
-                        "meson-allow-dirs-outside-of-prefix.patch"))))
+                "1gwba75z47m2hv3w08gw8sgqgbknjr7rj1qwr510bgknxwbjy8hn"))))
     (build-system python-build-system)
     (arguments
      `(;; FIXME: Tests require many additional inputs and patching many
@@ -309,10 +307,26 @@ files}, are written in a custom domain-specific language (@dfn{DSL}) that
 resembles Python.")
     (license license:asl2.0)))
 
+(define-public meson-0.60
+  (package
+    (inherit meson-0.63)
+    (version "0.60.3")
+    (source (origin
+              (method url-fetch)
+              (uri (string-append "https://github.com/mesonbuild/meson/"
+                                  "releases/download/" version  "/meson-"
+                                  version ".tar.gz"))
+              (sha256
+               (base32
+                "13mrrizg4vl6n5k7fz6amyafnn3i097dcarr552qc0ca6nlmzjl7"))
+              (patches (search-patches
+                        "meson-allow-dirs-outside-of-prefix.patch"))))))
+
 ;;; This older Meson variant is kept for now for gtkmm and others that may
 ;;; have problems with 0.60.
 (define-public meson-0.59
-  (package/inherit meson
+  (package
+    (inherit meson-0.60)
     (version "0.59.4")
     (source (origin
               (method url-fetch)
@@ -325,18 +339,8 @@ resembles Python.")
               (patches (search-patches
                         "meson-allow-dirs-outside-of-prefix.patch"))))))
 
-(define-public meson-0.63
-  (package
-    (inherit meson)
-    (version "0.63.2")
-    (source (origin
-              (method url-fetch)
-              (uri (string-append "https://github.com/mesonbuild/meson/"
-                                  "releases/download/" version  "/meson-"
-                                  version ".tar.gz"))
-              (sha256
-               (base32
-                "1gwba75z47m2hv3w08gw8sgqgbknjr7rj1qwr510bgknxwbjy8hn"))))))
+;; TODO: Bump this in the next rebuild cycle.
+(define-public meson meson-0.60)
 
 (define-public premake4
   (package