glibc: Include a copy of libgcc_s.so.1

This prevents failures like "libgcc_s.so.1 must be installed for
pthread_cancel to work" that occur because Glibc assumes libgcc_s.so.1
to be in Glibc's libdir.

This solution is pretty hacky, because the libgcc_s.so.1 from
bootstrap-tools might be too old. So if we update GCC, programs might
end up using an outdated libgcc_s.so.1. Ideally, we would build
libgcc_s.so.1 *before* Glibc, which might not be impossible...

Fixes #3548.

pkgs/development/libraries/glibc/builder.sh

@@ -46,10 +46,6 @@ postInstall() {
         ln -s lib $out/lib64
     fi
 
-    # This file, that should not remain in the glibc derivation,
-    # may have not been created during the preInstall
-    rm -f $out/lib/libgcc_s.so.1
-
     # Get rid of more unnecessary stuff.
     rm -rf $out/var $out/sbin/sln
 }

pkgs/development/libraries/glibc/default.nix

@@ -35,7 +35,7 @@ in
     preInstall = ''
       if [ -f ${stdenv.gcc.gcc}/lib/libgcc_s.so.1 ]; then
           mkdir -p $out/lib
-          ln -s ${stdenv.gcc.gcc}/lib/libgcc_s.so.1 $out/lib/libgcc_s.so.1
+          cp ${stdenv.gcc.gcc}/lib/libgcc_s.so.1 $out/lib/libgcc_s.so.1
       fi
     '';
 

pkgs/tools/filesystems/squashfs/default.nix

@@ -12,8 +12,6 @@ stdenv.mkDerivation rec {
   buildInputs = [ zlib xz ];
 
   preBuild = "cd squashfs-tools";
-  
-  NIX_LDFLAGS = "-lgcc_s"; # for pthread_cancel
 
   installFlags = "INSTALL_DIR=\${out}/bin";