ldso: preload standard path library with setuid bit set

ldso: preload standard path library with setuid bit set

For set-user-ID/set-group-ID ELF binaries, only libraries in the standard
search directories that are also set-user-ID must be loaded.
This patch fixes existing logic according to the above statement.
Furthermore if either library setuid bit isn't set or it cannot be found in
the standard search path, the library won't be preloaded but execution go
ahead with default one.

Signed-off-by: Filippo Arcidiacono <filippo.arcidiacono@st.com>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>