Do arquivo INSTALL no php-5.3.1.tar.gz:
13. Setup your php.ini file:
PHP will use the built-in default values if no php.ini file was
placed in the configuration directory. The default location is
/usr/local/lib, if you prefer your php.ini in another location, use
--with-config-file-path=/some/path in step 10.
The PHP distribution provides two sample php.ini files, you can use them
by
cp php.ini-development /usr/local/lib/php.ini
or
cp php.ini-production /usr/local/lib/php.ini
If you choose one of these php.ini files be certain to read the list
of changes within, as they affect how PHP behaves.
Você precisa criar o arquivo php.ini. Isso pode ser feito copiando um dos arquivos de amostra.