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end up using an outdated libgcc_s.so.1.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/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
     '';