make configure accept alternate gcc tuples for x32

the previous pattern required "x32" to be used as the second field of
the gcc tuple, which is usually reserved for vendor use and not
appropriate as an ABI specifier. with this change, putting "x32" at
the end of the tuple, the way ABI specifiers are normally done, is
also permitted.

configure

@@ -226,7 +226,7 @@ case "$target" in
 mips64*|powerpc64*) fail "$0: unsupported target \"$target\"" ;;
 arm*) ARCH=arm ;;
 i?86*) ARCH=i386 ;;
-x86_64-x32*|x32*) ARCH=x32 ;;
+x86_64-x32*|x32*|x86_64*x32) ARCH=x32 ;;
 x86_64*) ARCH=x86_64 ;;
 mips*) ARCH=mips ;;
 microblaze*) ARCH=microblaze ;;