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.

(cherry picked from commit d5bb6a1f9c0c099738a37ce2e923cd71d85b5145)

pkgs/build-support/cc-wrapper/ld-wrapper.sh

···
 
     # Finally, add `-rpath' switches.
     for i in $rpath; do
-        extra=(${extra[@]} -rpath $i)
+        extra+=(-rpath $i)
+    done
+fi
+
+
+# Only add --build-id if this is a final link. FIXME: should build gcc
+# with --enable-linker-build-id instead?
+if [ "$NIX_SET_BUILD_ID" = 1 ]; then
+    for p in "${params[@]}"; do
+        if [ "$p" = "-r" -o "$p" = "--relocatable" -o "$p" = "-i" ]; then
+            relocatable=1
+            break
+        fi
     done
+    if [ -z "$relocatable" ]; then
+        extra+=(--build-id)
+    fi
 fi
 
 

pkgs/build-support/setup-hooks/separate-debug-info.sh

···
-export NIX_LDFLAGS+=" --build-id --compress-debug-sections"
+export NIX_SET_BUILD_ID=1
+export NIX_LDFLAGS+=" --compress-debug-sections=zlib"
 export NIX_CFLAGS_COMPILE+=" -ggdb -Wa,--compress-debug-sections"
 dontStrip=1
 

pkgs/development/libraries/glibc/builder.sh

···
 
     # Get rid of more unnecessary stuff.
     rm -rf $out/var $out/sbin/sln
+
+    for i in $out/lib/*.a; do
+        strip -S "$i"
+    done
 }
 
 genericBuild

pkgs/development/libraries/glibc/default.nix

···
 , installLocales ? true
 , profilingLibraries ? false
 , gccCross ? null
-, debugSymbols ? false
 , withGd ? false, gd ? null, libpng ? null
 }:
 
···
   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;
···
       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 {})
 
   //