treewide: add meta.mainProgram to packages with a single binary

The nixpkgs-unstable channel's programs.sqlite was used to identify
packages producing exactly one binary, and these automatically added
to their package definitions wherever possible.

pkgs/development/tools/database/sqlcheck/default.nix

@@ -29,6 +29,7 @@ stdenv.mkDerivation rec {
   meta = with lib; {
     inherit (src.meta) homepage;
     description = "Automatically identify anti-patterns in SQL queries";
+    mainProgram = "sqlcheck";
     license = licenses.asl20;
     platforms = platforms.all;
     maintainers = [ maintainers.marsam ];