Several related solutions are found at unixpanic.com/modules.php.
I got the build to complete by finding a recent copy of instdso.sh on the web and installing it into /usr/lib/httpd/build/. The make install completed and left the new copy of libphp4.so in /usr/lib/httpd/modules. Now, all I have to do it to get it connected to Zend, then figure out how to build and install it on a Single Board Computer.
Hope this helps.