libc/glibc: add option to force unwind

We make it an option, as not all combinations of architectures
vs. compiler vs. glibc/eglibc exhibit the issue. Mostly visible
on old glibc versions, it seems...

This is a missing part from the glibc/eglibc merger... :-/

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;