Turn on --enable-new-dtags by default to make the linker set RUNPATH
instead of RPATH on binaries.  This is important because RUNPATH can
be overriden using LD_LIBRARY_PATH at runtime.

Patch from Nixpkgs by Eelco Dolstra <eelco.dolstra@logicblox.com>.

--- binutils/ld/ldmain.c
+++ binutils/ld/ldmain.c
@@ -296,6 +296,7 @@ main (int argc, char **argv)

   link_info.allow_undefined_version = TRUE;
   link_info.keep_memory = TRUE;
+  link_info.new_dtags = TRUE;
   link_info.combreloc = TRUE;
   link_info.strip_discarded = TRUE;
   link_info.callbacks = &link_callbacks;