build: reorder cxxflags in intrinsic checks
build: reorder cxxflags in intrinsic checks

Let the user have the final say in regards to using intrinsics.

Fixes: #13758
Alternaitve to #13789.

Xekyo/bitcoin,namecoin/namecore,namecoin/namecoin-core,fanquake/bitcoin,bitcoinsSG/bitcoin,sipsorcery/bitcoin,mruddy/bitcoin,kallewoof/bitcoin,jamesob/bitcoin,ajtowns/bitcoin,sstone/bitcoin,sstone/bitcoin,fujicoin/fujicoin,lateminer/bitcoin,bitcoin/bitcoin,sipsorcery/bitcoin,Xekyo/bitcoin,AkioNak/bitcoin,particl/particl-core,particl/particl-core,lateminer/bitcoin,fanquake/bitcoin,ajtowns/bitcoin,AkioNak/bitcoin,kallewoof/bitcoin,jamesob/bitcoin,mruddy/bitcoin,tecnovert/particl-core,namecoin/namecore,ajtowns/bitcoin,fujicoin/fujicoin,tecnovert/particl-core,kallewoof/bitcoin,bitcoin/bitcoin,namecoin/namecoin-core,particl/particl-core,sstone/bitcoin,Xekyo/bitcoin,mruddy/bitcoin,jambolo/bitcoin,namecoin/namecoin-core,particl/particl-core,sipsorcery/bitcoin,tecnovert/particl-core,Xekyo/bitcoin,fanquake/bitcoin,ajtowns/bitcoin,mruddy/bitcoin,fujicoin/fujicoin,fujicoin/fujicoin,jambolo/bitcoin,sipsorcery/bitcoin,jamesob/bitcoin,AkioNak/bitcoin,bitcoinsSG/bitcoin,ajtowns/bitcoin,jambolo/bitcoin,namecoin/namecore,jambolo/bitcoin,namecoin/namecoin-core,namecoin/namecoin-core,Xekyo/bitcoin,bitcoinsSG/bitcoin,sstone/bitcoin,namecoin/namecore,fujicoin/fujicoin,fanquake/bitcoin,mruddy/bitcoin,jambolo/bitcoin,bitcoinsSG/bitcoin,fanquake/bitcoin,tecnovert/particl-core,bitcoinsSG/bitcoin,namecoin/namecore,jamesob/bitcoin,sstone/bitcoin,particl/particl-core,sipsorcery/bitcoin,jamesob/bitcoin,Xekyo/bitcoin,kallewoof/bitcoin,mruddy/bitcoin,kallewoof/bitcoin,bitcoin/bitcoin,fujicoin/fujicoin,ajtowns/bitcoin,jamesob/bitcoin,AkioNak/bitcoin,particl/particl-core,bitcoin/bitcoin,jambolo/bitcoin,tecnovert/particl-core,AkioNak/bitcoin,lateminer/bitcoin,lateminer/bitcoin,kallewoof/bitcoin,sipsorcery/bitcoin,lateminer/bitcoin,fanquake/bitcoin,namecoin/namecoin-core,sstone/bitcoin,bitcoinsSG/bitcoin,bitcoin/bitcoin,AkioNak/bitcoin,tecnovert/particl-core,lateminer/bitcoin,namecoin/namecore,bitcoin/bitcoin