tools/flock: fix compile on Alpine Linux

fixes build errors:
src/flock.c:208:34: error: 'O_NOCTTY' undeclared (first use in this function)
     fd = open(filename, O_RDONLY|O_NOCTTY|O_CREAT, 0666);
src/flock.c:208:43: error: 'O_CREAT' undeclared (first use in this function)
     fd = open(filename, O_RDONLY|O_NOCTTY|O_CREAT, 0666);

Signed-off-by: Dirk Neukirchen <dirkneukirchen@web.de>

SVN-Revision: 48978