Before you can build everything, you'll need an ANSI/ISO C compiler. If your version of Solaris came with one, great. Otherwise, get gcc, the GNU C compiler. You can find information on how to get gcc from http://www.fsf.org/order/ftp.html.
By default, BIND assumes you're using the GNU C compiler and various other GNUish utilities, like flex and byacc. If your operating system came with a full complement of development tools, including cc, lex and yacc, you'll need to copy port/solaris/Makefile.set.sun to port/solaris/Makefile.set. This lets BIND know that you're using the stock tools.