When compiling PHP on a release FreeBSD 4.0 system (configured with this line :
./configure --with-mysql --enable-xml --enable-ftp --with-apache=../apache_1.3.12 )

I get this warning on multiple files when it is compiling libmysql:

In file included from FILENAME.c:##:
global.h:508: warning: useless keyword or type name in empty declaration
global.h:508: warning: empty declaration

The files include:
libmysql.c
errmsg.c
net.c
violite.c
password.c
my_init.c
my_static.c
my_malloc.c
my_realloc.c
my_create.c

and others.