By default gcc places 64 bit libs in a lib64 directory. This makes it use 
"lib" instead.

RP 25/7/10

Index: gcc-4.5.0/gcc/config/i386/t-linux64
===================================================================
--- gcc-4.5.0.orig/gcc/config/i386/t-linux64	2010-08-10 15:47:42.000000000 +0100
+++ gcc-4.5.0/gcc/config/i386/t-linux64	2010-08-10 15:47:47.000000000 +0100
@@ -24,8 +24,8 @@
 # MULTILIB_OSDIRNAMES according to what is found on the target.
 
 MULTILIB_OPTIONS = m64/m32
-MULTILIB_DIRNAMES = 64 32 
-MULTILIB_OSDIRNAMES = ../lib64 $(if $(wildcard $(shell echo $(SYSTEM_HEADER_DIR))/../../usr/lib32),../lib32,../lib)
+MULTILIB_DIRNAMES = . 32 
+MULTILIB_OSDIRNAMES = . $(if $(wildcard $(shell echo $(SYSTEM_HEADER_DIR))/../../usr/lib32),../lib32,../lib)
 
 LIBGCC = stmp-multilib
 INSTALL_LIBGCC = install-multilib
Index: gcc-4.5.0/gcc/config/i386/linux64.h
===================================================================
--- gcc-4.5.0.orig/gcc/config/i386/linux64.h	2010-08-10 15:49:06.000000000 +0100
+++ gcc-4.5.0/gcc/config/i386/linux64.h	2010-08-10 15:49:16.000000000 +0100
@@ -59,7 +59,7 @@
    done.  */
 
 #define GLIBC_DYNAMIC_LINKER32 "/lib/ld-linux.so.2"
-#define GLIBC_DYNAMIC_LINKER64 "/lib64/ld-linux-x86-64.so.2"
+#define GLIBC_DYNAMIC_LINKER64 "/lib/ld-linux-x86-64.so.2"
 
 #if TARGET_64BIT_DEFAULT
 #define SPEC_32 "m32"
