build: add a way to specify the list of build artifacts
build: add a way to specify the list of build artifacts

If you don't want to build eveything, you can narrow down the list of
artifacts liek this:

 $ ./configure --with tests/test-reactor --with apps/httpd/httpd

wildinto/scylla,dwdm/scylla,chunshengster/seastar,stamhe/seastar,eklitzke/scylla,acbellini/seastar,avikivity/scylla,aruanruan/scylla,wildinto/scylla,capturePointer/scylla,avikivity/seastar,norcimo5/seastar,scylladb/scylla,kangkot/scylla,kjniemi/scylla,ducthangho/imdb,raphaelsc/seastar,scylladb/seastar,raphaelsc/scylla,shyamalschandra/seastar,stamhe/scylla,ducthangho/imdb,bzero/seastar,victorbriz/scylla,jonathanleang/seastar,leejir/seastar,linearregression/seastar,wildinto/seastar,senseb/scylla,avikivity/scylla,guiquanz/scylla,tempbottle/scylla,dreamsxin/seastar,duarten/scylla,kjniemi/seastar,eklitzke/scylla,xtao/seastar,syuu1228/seastar,norcimo5/seastar,dwdm/scylla,flashbuckets/seastar,syuu1228/seastar,acbellini/scylla,scylladb/scylla,rluta/scylla,linearregression/seastar,printedheart/seastar,koolhazz/seastar,gwicke/scylla,printedheart/seastar,kjniemi/seastar,rluta/scylla,glommer/scylla,bzero/seastar,hongliangzhao/seastar,slivne/seastar,bowlofstew/scylla,cloudius-systems/seastar,xtao/seastar,dwdm/seastar,avikivity/seastar,slivne/seastar,bowlofstew/seastar,linearregression/scylla,justintung/scylla,justintung/scylla,stamhe/seastar,koolhazz/seastar,anzihenry/seastar,stamhe/seastar,acbellini/seastar,tempbottle/scylla,sjperkins/seastar,anzihenry/seastar,jonathanleang/seastar,raphaelsc/seastar,rentongzhang/scylla,hongliangzhao/seastar,kjniemi/seastar,victorbriz/scylla,hongliangzhao/seastar,bzero/seastar,wildinto/seastar,leejir/seastar,avikivity/scylla,asias/scylla,printedheart/seastar,bowlofstew/scylla,shyamalschandra/seastar,wildinto/seastar,duarten/scylla,kangkot/scylla,flashbuckets/seastar,bowlofstew/scylla,asias/scylla,linearregression/scylla,chunshengster/seastar,senseb/scylla,acbellini/scylla,asias/scylla,mixja/seastar,mixja/seastar,tempbottle/seastar,tempbottle/scylla,scylladb/scylla-seastar,shaunstanislaus/scylla,scylladb/seastar,scylladb/scylla,respu/scylla,kangkot/scylla,chunshengster/seastar,scylladb/scylla-seastar,anzihenry/seastar,bowlofstew/seastar,jonathanleang/seastar,acbellini/scylla,dreamsxin/seastar,norcimo5/seastar,joerg84/seastar,sjperkins/seastar,glommer/scylla,scylladb/scylla,phonkee/scylla,flashbuckets/seastar,raphaelsc/seastar,wildinto/scylla,shaunstanislaus/scylla,kjniemi/scylla,slivne/seastar,rentongzhang/scylla,dreamsxin/seastar,shyamalschandra/seastar,ducthangho/imdb,xtao/seastar,shaunstanislaus/scylla,scylladb/seastar,eklitzke/scylla,acbellini/seastar,respu/scylla,senseb/scylla,dwdm/seastar,linearregression/seastar,phonkee/scylla,tempbottle/seastar,duarten/scylla,koolhazz/seastar,cloudius-systems/seastar,guiquanz/scylla,justintung/scylla,cloudius-systems/seastar,avikivity/seastar,kjniemi/scylla,linearregression/scylla,gwicke/scylla,syuu1228/seastar,raphaelsc/scylla,raphaelsc/scylla,aruanruan/scylla,rentongzhang/scylla,bowlofstew/seastar,dwdm/seastar,capturePointer/scylla,joerg84/seastar,capturePointer/scylla,stamhe/scylla,mixja/seastar,rluta/scylla,stamhe/scylla,tempbottle/seastar,phonkee/scylla,leejir/seastar,joerg84/seastar,dwdm/scylla,glommer/scylla,sjperkins/seastar,scylladb/scylla-seastar,aruanruan/scylla,guiquanz/scylla,victorbriz/scylla,respu/scylla,gwicke/scylla