build: fix warning detection on gcc
build: fix warning detection on gcc

gcc ignores -Wno-mismatches-tags even though it is not supported.  Invert
the sense of the warning for the test.

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