treewide: fix some comments (#247365)

* pkgs/top-level/splice.nix: fix broken comment

* stdenv: use a value that actually works in the comment there

pkgs/stdenv/generic/make-derivation.nix

@@ -48,7 +48,7 @@ let
 
     in finalPackage;
 
-  # makeDerivationExtensibleConst == makeDerivationExtensible (_: attrs),
+  #makeDerivationExtensibleConst = attrs: makeDerivationExtensible (_: attrs);
   # but pre-evaluated for a slight improvement in performance.
   makeDerivationExtensibleConst = attrs:
     mkDerivationSimple

pkgs/top-level/splice.nix

@@ -6,10 +6,10 @@
 # run-time) of a package to a consumer that isn't used to thinking so cleverly.
 #
 # The solution is to splice the package sets together as we do below, so every
-# `callPackage`d expression in fact gets both versions. Each# derivation (and
-# each derivation's outputs) consists of the run-time version, augmented with a
-# `__spliced.buildHost` field for the build-time version, and `__spliced.hostTarget` field for the
-# run-time version.
+# `callPackage`d expression in fact gets both versions. Each derivation (and
+# each derivation's outputs) consists of the run-time version, augmented with
+# a `__spliced.buildHost` field for the build-time version, and
+# `__spliced.hostTarget` field for the run-time version.
 #
 # For performance reasons, rather than uniformally splice in all cases, we only
 # do so when `pkgs` and `buildPackages` are distinct. The `actuallySplice`