scripts: correctly warn when the local tarballs directory does not exist

Warn about a missing local tarball directory, only if it was configured.
Avoid the spurious message:
Directory '${CT_LOCAL_TARBALLS_DIR}' does not exist.
Will not save downloaded tarballs to local storage.

Thanks to "Pedro I. Sanchez" <psanchez@colcan.ca> for pointing out the
issue:
http://sourceware.org/ml/crossgcc/2009-12/msg00011.html

--- binutils/ld/emulparams/elf_i386.sh

+++ binutils/ld/emulparams/elf_i386.sh

@@ -13,3 +13,13 @@

 NO_SMALL_DATA=yes

 SEPARATE_GOTPLT=12

 IREL_IN_PLT=

+

+# In Gentoo, we install 32bit libs into /lib32 in an

+# ABI setup with amd64/x86

+case "$target" in

+  x86_64*-linux*)

+    case "$EMULATION_NAME" in

+      *i386*) LIBPATH_SUFFIX=32  ;;

+    esac

+  ;;

+esac