configure: support biarch builds with --multiarch=lib64

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/configure b/configure
index 965fe6b..19e8d82 100755
--- a/configure
+++ b/configure
@@ -11379,8 +11379,13 @@
 
 # Check whether --with-multiarch was given.
 if test "${with_multiarch+set}" = set; then :
-  withval=$with_multiarch; libdir=$libdir/$withval
-root_libdir=$root_libdir/$withval
+  withval=$with_multiarch; if test "$withval" = "lib64"; then
+    libdir=/usr/lib64
+    root_libdir=/lib64
+else
+    libdir=$libdir/$withval
+    root_libdir=$root_libdir/$withval
+fi
 
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether we can link with -static" >&5