libc/glibc: use the common start_files procedure

Use the common procedure, shared between glibc and eglibc. This requires
that glibc-specific bits be included in the shared procedure.

But still build the full libc with the glibc-specific procedure. This will
be commonalised in a future commit.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

--- binutils/ld/ldmain.c

+++ binutils/ld/ldmain.c

@@ -293,2 +293,3 @@ main (int argc, char **argv)

   link_info.combreloc = TRUE;

+  link_info.relro = TRUE;

   link_info.strip_discarded = TRUE;