pahole: 1.17 -> 1.20

Also:
 - make fetchSubodules explicit, it is strictly required by pahole
build system until debian efforts to use system libbpf finish:
see https://www.spinics.net/lists/dwarves/msg00732.html

 - fix license to gpl2Only as requested by review bot

pkgs/development/tools/misc/pahole/default.nix

@@ -2,11 +2,12 @@
 
 stdenv.mkDerivation rec {
   pname = "pahole";
-  version = "1.17";
+  version = "1.20";
   src = fetchgit {
     url = "https://git.kernel.org/pub/scm/devel/pahole/pahole.git";
     rev = "v${version}";
-    sha256 = "13dxsmhpf9n2wqggf4gd6f12rm0vhv0q96jd50gkvaxzzvgpzzbc";
+    sha256 = "11q9dpfi4qj2v8z0nlf8c0079mlv10ljhh0d1yr0j4ds3saacd15";
+    fetchSubmodules = true;
   };
 
   nativeBuildInputs = [ cmake ];
@@ -18,7 +19,7 @@ stdenv.mkDerivation rec {
   meta = with lib; {
     homepage = "https://git.kernel.org/cgit/devel/pahole/pahole.git/";
     description = "Pahole and other DWARF utils";
-    license = licenses.gpl2;
+    license = licenses.gpl2Only;
 
     platforms = platforms.linux;
     maintainers = [ maintainers.bosu ];