glibc: Enable separate debug symbols

The importance of glibc makes it worthwhile to provide debug
symbols. However, this revealed an issue with separateDebugInfo: it
was indiscriminately adding --build-id to all ld invocations, while in
fact it should only do that for final links. Glibc also uses non-final
("relocatable") links, leading to subsequent failure to apply a build
ID ("Cannot create .note.gnu.build-id section, --build-id
ignored"). So now ld-wrapper.sh only passes --build-id for final
links.

pkgs/development/libraries/glibc/default.nix

@@ -2,7 +2,6 @@
 , installLocales ? true
 , profilingLibraries ? false
 , gccCross ? null
-, debugSymbols ? false
 , withGd ? false, gd ? null, libpng ? null
 }:
 
@@ -13,9 +12,7 @@ let
   cross = if gccCross != null then gccCross.target else null;
 in
   build cross ({
-    name = "glibc"
-      + lib.optionalString debugSymbols "-debug"
-      + lib.optionalString withGd "-gd";
+    name = "glibc" + lib.optionalString withGd "-gd";
 
     inherit lib stdenv fetchurl linuxHeaders installLocales
       profilingLibraries gccCross withGd gd libpng;
@@ -38,23 +35,13 @@ in
       fi
     '';
 
+    separateDebugInfo = true;
+
     meta.description = "The GNU C Library";
   }
 
   //
 
-  (if debugSymbols
-   then {
-     # Build with debugging symbols, but leave optimizations on and don't
-     # attempt to keep the build tree.
-     dontStrip = true;
-     dontCrossStrip = true;
-     NIX_STRIP_DEBUG = 0;
-   }
-   else {})
-
-  //
-
   (if cross != null
    then {
       preConfigure = ''