KADM5 support is disabled by default, enable it passing --with-krb5kadm to configure. KADM5 support uses some interal header files of the MIT krb5 distribution. These headers are bundled but you can specify another source (which needs to be a unpacked krb5 distribution with configure and make run) giving a path to the switch.
When compiling this extension as shared module:
run phpize in the extension directory
run ./configure (optionally add --with-krb5kadm if you need this functionality)
run make && make install
optional: enable your new extension in you php.ini by adding extension=krb5.so to it.
When compiling statically into your php binary:
move this extension into your php distributions ext/ folder
make sure that the directory is named "krb5"
run ./buildconf --force in the root directory of you php distribution
./configure php with your common flags and add --with-krb5 and optionally --with-krb5kadm=<path> where <path> is the path to your mit-krb5 distribution.
make && make install