treewide: fix various links (homepage, src)

pkgs/development/libraries/libsigcxx/1.2.nix

@@ -12,7 +12,7 @@ stdenv.mkDerivation rec {
   buildInputs = [ m4];
 
   meta = {
-    homepage = http://libsigc.sourceforge.net/;
+    homepage = https://libsigcplusplus.github.io/libsigcplusplus/;
     description = "A typesafe callback system for standard C++";
     branch = "1.2";
     platforms = stdenv.lib.platforms.unix;

pkgs/development/libraries/libsigcxx/default.nix

@@ -16,7 +16,7 @@ stdenv.mkDerivation rec {
   doCheck = true;
 
   meta = with stdenv.lib; {
-    homepage = http://libsigc.sourceforge.net/;
+    homepage = https://libsigcplusplus.github.io/libsigcplusplus/;
     description = "A typesafe callback system for standard C++";
     license = licenses.lgpl21;
     platforms = platforms.all;