complibs/libelf: build with -fPIC

libelf is used by gcc to build the lto-plugin used
by binutils' gold to perform LTO.

This requires that files in libelf be compiled with
-fPIC to generate a proper .so.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
(transplanted from c48aba92cbeb7b7dce956a63ec65d3296735cc16)

--- 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;