Also search the LICENSE file in lib64/pythonX.Y

Several Linux distributions including Gentoo, Fedora, openSUSE
put things in lib64/pythonX.Y instead of lib/pythonX.Y on 64bit
architectures (x86_64, aarch64, etc.).

This was already respected via the fix_lib64() function, however
when virtualenv was searching for Python LICENSE, it was not.

Now is the lib64/pythonX.Y patch searched as well and unlike fix_lib64()
no checks need to be made, as the patch are tested in sequence.

See pypa#1352 (comment)

virtualenv.py

@@ -1333,9 +1333,12 @@ def copy_required_files(src_dir, lib_dir, symlink):
 
 def copy_license(prefix, dst_prefix, lib_dir, symlink):
     """Copy the license file so `license()` builtin works"""
+    lib64_dir = lib_dir.replace("lib", "lib64")
     for license_path in (
         # posix cpython
         os.path.join(prefix, os.path.relpath(lib_dir, dst_prefix), "LICENSE.txt"),
+        # posix cpython installed in /usr/lib64
+        os.path.join(prefix, os.path.relpath(lib64_dir, dst_prefix), "LICENSE.txt"),
         # windows cpython
         os.path.join(prefix, "LICENSE.txt"),
         # pypy