configure: prefer lib64 on 64-bit platforms

use lib64 if
- "/usr/lib/multi-arch-triplet" does not work and
- we are on a 64-bit platform and
- lib64 exists and does contain crti.o

configure

@@ -325,10 +325,12 @@ if test -z "$cross_prefix" ; then
       fi
 
       if test -z "$triplet"; then
-        if test ! -f "/usr/lib/crti.o" -a -f "/usr/lib64/crti.o" ; then
+        if test $cpu = "x86-64" -o $cpu = "aarch64" ; then
+          if test -f "/usr/lib64/crti.o" ; then
             tcc_lddir="lib64"
           fi
         fi
+      fi
 
       if test "$cpu" = "armv4l" ; then
 	if test "${triplet%eabihf}" != "$triplet" ; then
@@ -401,7 +403,6 @@ prefix=$prefix
 bindir=\$(DESTDIR)$bindir
 tccdir=\$(DESTDIR)$tccdir
 libdir=\$(DESTDIR)$libdir
-ln_libdir=$libdir
 includedir=\$(DESTDIR)$includedir
 mandir=\$(DESTDIR)$mandir
 infodir=\$(DESTDIR)$infodir