build: fix libnatpmp macos cross compile
build: fix libnatpmp macos cross compile

Currently, our cross-compile of libnatpmp for macOS doesn't work at all.
The wrong archiver is used, which produces an archive the linker doesn't like.
This becomes clear when configuring:
```bash
configure:25722: checking for initnatpmp in -lnatpmp
configure:25747: env -u C_INCLUDE_PATH -u CPLUS_INCLUDE_PATH -u OBJC_INCLUDE_PATH -u OBJCPLUS_INCLUDE_PATH -u CPATH -u LIBRARY_PATH /home/ubuntu/bitcoin/depends/x86_64-apple-darwin18/native/bin/clang++ --target=x86_64-apple-darwin18 <trim>  -Wl,-headerpad_max_install_names -Wl,-dead_strip -Wl,-dead_strip_dylibs conftest.cpp -lnatpmp   >&5
ld: archive has no table of contents for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
```

Fix this by using the right `ar` (we do the same for upnp).

While we're at it, we fixe the build so that we are using our c/ppflags.
This  means building with `-O2` rather than `-Os`.

Note that this fixes an issue that is also fixed by #21209.
However, given there are reservations about updating to use a newer libnatpmp source, we should just fix this for now.

sstone/bitcoin,MeshCollider/bitcoin,bitcoinsSG/bitcoin,ElementsProject/elements,anditto/bitcoin,MarcoFalke/bitcoin,prusnak/bitcoin,bitcoinknots/bitcoin,n1bor/bitcoin,ajtowns/bitcoin,MarcoFalke/bitcoin,JeremyRubin/bitcoin,sipsorcery/bitcoin,namecoin/namecore,GroestlCoin/GroestlCoin,bitcoinknots/bitcoin,apoelstra/bitcoin,domob1812/bitcoin,ajtowns/bitcoin,prusnak/bitcoin,qtumproject/qtum,Sjors/bitcoin,rnicoll/bitcoin,Xekyo/bitcoin,bitcoin/bitcoin,andreaskern/bitcoin,andreaskern/bitcoin,MeshCollider/bitcoin,namecoin/namecore,qtumproject/qtum,domob1812/namecore,Sjors/bitcoin,GroestlCoin/bitcoin,JeremyRubin/bitcoin,apoelstra/bitcoin,domob1812/namecore,sipsorcery/bitcoin,lateminer/bitcoin,ElementsProject/elements,dscotese/bitcoin,tecnovert/particl-core,pataquets/namecoin-core,jambolo/bitcoin,fanquake/bitcoin,domob1812/namecore,domob1812/bitcoin,andreaskern/bitcoin,sstone/bitcoin,apoelstra/bitcoin,n1bor/bitcoin,prusnak/bitcoin,bitcoin/bitcoin,pataquets/namecoin-core,rnicoll/bitcoin,AkioNak/bitcoin,Xekyo/bitcoin,andreaskern/bitcoin,tecnovert/particl-core,namecoin/namecore,Xekyo/bitcoin,rnicoll/bitcoin,namecoin/namecore,instagibbs/bitcoin,apoelstra/bitcoin,ajtowns/bitcoin,dscotese/bitcoin,jamesob/bitcoin,GroestlCoin/bitcoin,jlopp/statoshi,bitcoinsSG/bitcoin,namecoin/namecoin-core,domob1812/bitcoin,particl/particl-core,prusnak/bitcoin,bitcoinsSG/bitcoin,dscotese/bitcoin,pataquets/namecoin-core,bitcoinknots/bitcoin,qtumproject/qtum,dscotese/bitcoin,domob1812/bitcoin,pataquets/namecoin-core,AkioNak/bitcoin,lateminer/bitcoin,namecoin/namecore,JeremyRubin/bitcoin,prusnak/bitcoin,domob1812/namecore,sstone/bitcoin,anditto/bitcoin,rnicoll/bitcoin,sipsorcery/bitcoin,sstone/bitcoin,jlopp/statoshi,n1bor/bitcoin,yenliangl/bitcoin,lateminer/bitcoin,MeshCollider/bitcoin,fanquake/bitcoin,instagibbs/bitcoin,MarcoFalke/bitcoin,jamesob/bitcoin,kallewoof/bitcoin,fujicoin/fujicoin,fujicoin/fujicoin,bitcoin/bitcoin,apoelstra/bitcoin,domob1812/namecore,dscotese/bitcoin,anditto/bitcoin,fanquake/bitcoin,dscotese/bitcoin,pataquets/namecoin-core,jlopp/statoshi,pataquets/namecoin-core,bitcoinknots/bitcoin,mm-s/bitcoin,JeremyRubin/bitcoin,domob1812/bitcoin,andreaskern/bitcoin,AkioNak/bitcoin,MarcoFalke/bitcoin,ElementsProject/elements,namecoin/namecore,jamesob/bitcoin,rnicoll/bitcoin,particl/particl-core,fujicoin/fujicoin,fanquake/bitcoin,particl/particl-core,mm-s/bitcoin,GroestlCoin/GroestlCoin,jlopp/statoshi,particl/particl-core,MarcoFalke/bitcoin,AkioNak/bitcoin,AkioNak/bitcoin,bitcoin/bitcoin,GroestlCoin/GroestlCoin,bitcoin/bitcoin,ajtowns/bitcoin,JeremyRubin/bitcoin,GroestlCoin/bitcoin,lateminer/bitcoin,prusnak/bitcoin,fujicoin/fujicoin,mm-s/bitcoin,fanquake/bitcoin,achow101/bitcoin,qtumproject/qtum,JeremyRubin/bitcoin,n1bor/bitcoin,ElementsProject/elements,anditto/bitcoin,MarcoFalke/bitcoin,bitcoinsSG/bitcoin,jambolo/bitcoin,lateminer/bitcoin,mruddy/bitcoin,GroestlCoin/bitcoin,GroestlCoin/bitcoin,mruddy/bitcoin,achow101/bitcoin,AkioNak/bitcoin,rnicoll/bitcoin,GroestlCoin/GroestlCoin,fanquake/bitcoin,mruddy/bitcoin,namecoin/namecoin-core,jambolo/bitcoin,domob1812/namecore,GroestlCoin/GroestlCoin,namecoin/namecoin-core,yenliangl/bitcoin,particl/particl-core,jlopp/statoshi,mruddy/bitcoin,instagibbs/bitcoin,jamesob/bitcoin,MeshCollider/bitcoin,Sjors/bitcoin,ElementsProject/elements,tecnovert/particl-core,Xekyo/bitcoin,particl/particl-core,namecoin/namecoin-core,yenliangl/bitcoin,Xekyo/bitcoin,domob1812/bitcoin,achow101/bitcoin,tecnovert/particl-core,bitcoinknots/bitcoin,lateminer/bitcoin,MeshCollider/bitcoin,kallewoof/bitcoin,jambolo/bitcoin,ajtowns/bitcoin,Sjors/bitcoin,qtumproject/qtum,ajtowns/bitcoin,yenliangl/bitcoin,fujicoin/fujicoin,jamesob/bitcoin,jlopp/statoshi,yenliangl/bitcoin,fujicoin/fujicoin,jamesob/bitcoin,andreaskern/bitcoin,apoelstra/bitcoin,sstone/bitcoin,bitcoin/bitcoin,namecoin/namecoin-core,mm-s/bitcoin,n1bor/bitcoin,n1bor/bitcoin,tecnovert/particl-core,Xekyo/bitcoin,anditto/bitcoin,bitcoinsSG/bitcoin,kallewoof/bitcoin,sstone/bitcoin,tecnovert/particl-core,sipsorcery/bitcoin,instagibbs/bitcoin,mruddy/bitcoin,GroestlCoin/GroestlCoin,sipsorcery/bitcoin,qtumproject/qtum,mm-s/bitcoin,instagibbs/bitcoin,jambolo/bitcoin,achow101/bitcoin,qtumproject/qtum,bitcoinsSG/bitcoin,GroestlCoin/bitcoin,achow101/bitcoin,ElementsProject/elements,yenliangl/bitcoin,instagibbs/bitcoin,achow101/bitcoin,MeshCollider/bitcoin,mm-s/bitcoin,anditto/bitcoin,kallewoof/bitcoin,mruddy/bitcoin,sipsorcery/bitcoin,kallewoof/bitcoin,kallewoof/bitcoin,Sjors/bitcoin,jambolo/bitcoin,namecoin/namecoin-core