txt2man: minor cleanups, don't overwrite patchPhase, use makeFlags directly

pkgs/tools/misc/txt2man/default.nix

@@ -11,19 +11,19 @@ stdenv.mkDerivation rec {
     hash = "sha256-Aqi5PNNaaM/tr9A/7vKeafYKYIs/kHbwHzE7+R/9r9s=";
   };
 
-  preConfigure = ''
-    makeFlags=prefix="$out"
-  '';
+  makeFlags = [
+    "prefix=${placeholder "out"}"
+  ];
 
-  patchPhase = ''
+  postPatch = ''
     for f in bookman src2man txt2man; do
-        substituteInPlace $f --replace "gawk" "${gawk}/bin/gawk"
-
-        substituteInPlace $f --replace "(date" "(${coreutils}/bin/date"
-        substituteInPlace $f --replace "=cat" "=${coreutils}/bin/cat"
-        substituteInPlace $f --replace "cat <<" "${coreutils}/bin/cat <<"
-        substituteInPlace $f --replace "expand" "${coreutils}/bin/expand"
-        substituteInPlace $f --replace "(uname" "(${coreutils}/bin/uname"
+      substituteInPlace $f \
+        --replace "gawk" "${gawk}/bin/gawk" \
+        --replace "(date" "(${coreutils}/bin/date" \
+        --replace "=cat" "=${coreutils}/bin/cat" \
+        --replace "cat <<" "${coreutils}/bin/cat <<" \
+        --replace "expand" "${coreutils}/bin/expand" \
+        --replace "(uname" "(${coreutils}/bin/uname"
     done
   '';
 
@@ -35,11 +35,11 @@ stdenv.mkDerivation rec {
     sh -c 'unset PATH; printf hello | ./txt2man'
   '';
 
-  meta = {
+  meta = with lib; {
     description = "Convert flat ASCII text to man page format";
     homepage = "http://mvertes.free.fr/";
-    license = lib.licenses.gpl2;
-    platforms = with lib.platforms; linux ++ darwin;
-    maintainers = with lib.maintainers; [ bjornfor ];
+    license = licenses.gpl2;
+    platforms = platforms.unix;
+    maintainers = with maintainers; [ bjornfor ];
   };
 }