Turn some license strings into lib.licenses values

pkgs/os-specific/windows/jom/default.nix

@@ -31,6 +31,6 @@ stdenv.mkDerivation {
   meta = {
     homepage = http://qt-project.org/wiki/jom;
     description = "Clone of nmake supporting multiple independent commands in parallel";
-    license = "GPLv2+"; # Explicitly, GPLv2 or GPLv3, but not later.
+    license = stdenv.lib.licenses.gpl2Plus; # Explicitly, GPLv2 or GPLv3, but not later.
   };
 }

pkgs/os-specific/windows/pthread-w32/default.nix

@@ -56,6 +56,6 @@ stdenv.mkDerivation {
 
     homepage = http://sourceware.org/pthreads-win32/;
 
-    license = "LGPLv2.1+";
+    license = stdenv.lib.licenses.lgpl21Plus;
   };
 }