gcc  -I. -I/u2/nobackup/tmp/php-4.0.4pl1/ext/sockets -I/u2/nobackup/tmp/php-4.0.4pl1/main -I/u2/nobackup/tmp/php-4.0.4pl1 -I/u2/nobackup/tmp/php-4.0.4pl1/Zend  -I/usr/local/include/freetype -I/usr/local/gd/include -I/u2/nobackup/tmp/php-4.0.4pl1/ext/mysql/libmysql -I/u2/nobackup/tmp/php-4.0.4pl1/ext/xml/expat/xmltok -I/u2/nobackup/tmp/php-4.0.4pl1/ext/xml/expat/xmlparse -I/u2/nobackup/tmp/php-4.0.4pl1/TSRM  -DXML_BYTE_ORDER=12 -g -O2 -belf  -c sockets.c && touch sockets.lo
sockets.c: In function `php_if_bind':
sockets.c:1140: `h_errno' undeclared (first use in this function)
[...]
make[1]: *** [sockets.lo] Error 1

After adding "int h_errno;" to sockets.c:

gcc  -I. -I/u2/nobackup/tmp/php-4.0.4pl1/ext/sockets -I/u2/nobackup/tmp/php-4.0.4pl1/main -I/u2/nobackup/tmp/php-4.0.4pl1 -I/u2/nobackup/tmp/php-4.0.4pl1/Zend -I/usr/local/include/freetype -I/usr/local/gd/include -I/u2/nobackup/tmp/php-4.0.4pl1/ext/mysql/libmysql -I/u2/nobackup/tmp/php-4.0.4pl1/ext/xml/expat/xmltok -I/u2/nobackup/tmp/php-4.0.4pl1/ext/xml/expat/xmlparse -I/u2/nobackup/tmp/php-4.0.4pl1/TSRM  -DXML_BYTE_ORDER=12 -g -O2 -belf  -c sockets.c && touch sockets.lo
In file included from /usr/include/sys/ucontext.h:22,
                 from /usr/include/sys/signal.h:364,
                 from /usr/include/xpg4v2/signal.h:35,
                 from /usr/include/signal.h:7,
                 from sockets.c:49:
/usr/include/sys/regset.h:41: redefinition of `struct _fpstate'
[...]
make[1]: *** [sockets.lo] Error 1

After temporarily removing any mentioning of _fpstate from
/usr/include/sys/regset.h:

gcc [...]   -o php -export-dynamic      stub.lo libphp4.la
Undefined                       first referenced
 symbol                             in file
SUN_LEN                             .libs/libphp4.a(sockets.o)
php: fatal error: Symbol referencing errors. No output written to php

After  adding "#define SUN_LEN(a)    sizeof(*a)" to sockets.c, it compiles fine

Configuration options:
./configure  --with-gd=/usr/local/gd --with-mysql --enable-sockets