systemtap-sdt: init

This is an API-stable alias for "systemtap *just* for creating trace
points". The use case for this is that the main systemtap package has an
annoyingly large closure size of Linux version dependent stuff, which is
unnecessary for building trace points.

I am adding this after needing the same override for Lix.

pkgs/by-name/gl/glib/package.nix

···
     else
       "2.0-0.lib";
 
-  systemtap' = buildPackages.linuxPackages.systemtap.override { withStap = false; };
+  systemtap' = buildPackages.systemtap-sdt;
 
   withDtrace =
     lib.meta.availableOn stdenv.buildPlatform systemtap'

pkgs/by-name/sy/systemtap-sdt/package.nix

···
+{ linuxPackages }:
+linuxPackages.systemtap.override {
+  withStap = false;
+}
+// {
+  meta = linuxPackages.systemtap.meta // {
+    description = "Build USDT tracepoints with the 'dtrace' executable on Linux";
+    mainProgram = "dtrace";
+  };
+}

pkgs/development/tools/profiling/systemtap/default.nix

···
   gnumake,
   python3,
   nixosTests,
-  withStap ? true, # avoid cyclic dependency with glib
+  withStap ? true, # avoid cyclic dependency with glib, reduce closure size substantially
 }:
 
 let