I was unable to build ARP-1.0.0 on CYGWIN.  I get the following error:
 
$ make
make[1]: Entering directory `/cygdrive/y/spryware/apr/apr-1.0.0'
/bin/bash /cygdrive/y/spryware/apr/apr-1.0.0/libtool --silent --mode=compile gcc -g -O2   -DHAVE_CON
FIG_H -DCYGWIN   -I./include -I/cygdrive/y/spryware/apr/apr-1.0.0/include/arch/unix -I./include/arch
/unix -I/cygdrive/y/spryware/apr/apr-1.0.0/include  -o network_io/unix/sockopt.lo -c network_io/unix
/sockopt.c && touch network_io/unix/sockopt.lo
network_io/unix/sockopt.c: In function `apr_socket_opt_set':
network_io/unix/sockopt.c:135: error: `ttllevel' undeclared (first use in this function)
network_io/unix/sockopt.c:135: error: (Each undeclared identifier is reported only once
network_io/unix/sockopt.c:135: error: for each function it appears in.)
network_io/unix/sockopt.c:136: error: `ttl' undeclared (first use in this function)
make[1]: *** [network_io/unix/sockopt.lo] Error 1
make[1]: Leaving directory `/cygdrive/y/spryware/apr/apr-1.0.0'
make: *** [all-recursive] Error 1
 
Daniel May