configure: fix broken test Since commit d1807a4f836c27f6dc7061e53a834dd27f78e46a ./configure tries to test files and directories with "test -f", which only test for regular files. Test with "test -e", which looks for any kind of files. This unbreak the configure script when not using a separate object directory. Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>