Add targets to simplify building PHP with FDO (Feedback Directed Optimisation)

Add targets to simplify building PHP with FDO (Feedback Directed Optimisation)
PHP should be built with the folowing steps:

make clean
make -j4 prof-gen
; now php should be trained with some scripts
; for example `sapi/cgi/php -T 1000 /var/www/http/wordpress/index.php > /dev/null`
make prof-clean
make -j4 prof-use

The "properly" trained build may give up to 10% real performance boost!
"Improprly" trained PHP might be even slower.