scripts: always create lib32 and lib64 symlinks

Unconditionally create the lib32 -> lib/ and lib64 -> lib/ symlinks.

This is reportedly a fix to build a toolchain for a 32-bit target on
a 'pure' 64-bit host (eg. on Fedora FC12, host libs are in lib64/,
and there is no lib -> lib64 symlink, as we can see on other distors,
as Debian). As gcc only puts static host lib in lib64/ (along with
target files in subdirs), we can safely create the symlinks.

Also note that the symlinks are summarily removed at the end
of the build.

Signed-off-by: Anthony Foiani <anthony.foiani@gmail.com>
[Yann E. MORIN: fix a comment, rephrase the commit log]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

Original patch from gentoo: gentoo/src/patchsets/gcc/4.3.1/uclibc/90_all_301-missing-execinfo_h.patch

diff -durN gcc-4.3.1.orig/boehm-gc/include/gc.h gcc-4.3.1/boehm-gc/include/gc.h

--- gcc-4.3.1.orig/boehm-gc/include/gc.h	2007-04-23 23:10:09.000000000 +0200

+++ gcc-4.3.1/boehm-gc/include/gc.h	2008-06-10 14:58:54.000000000 +0200

@@ -503,7 +503,7 @@

 #if defined(__linux__) || defined(__GLIBC__)

 # include <features.h>

 # if (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 1 || __GLIBC__ > 2) \

-     && !defined(__ia64__)

+     && !defined(__ia64__) && !defined(__UCLIBC__)

 #   ifndef GC_HAVE_BUILTIN_BACKTRACE

 #     define GC_HAVE_BUILTIN_BACKTRACE

 #   endif