spark2014: do not hardcode gnat12 version

Fixes #238644

pkgs/development/libraries/ada/spark2014/default.nix

···
 
   postPatch = ''
     # gnat2why/gnat_src points to the GNAT sources
-    tar xf ${gnat12.cc.src} gcc-12.2.0/gcc/ada
-    mv gcc-12.2.0/gcc/ada gnat2why/gnat_src
+    tar xf ${gnat12.cc.src} gcc-${gnat12.cc.version}/gcc/ada
+    mv gcc-${gnat12.cc.version}/gcc/ada gnat2why/gnat_src
   '';
 
   configurePhase = ''