bitcoin: Requires macOS 10.15 or later

See: https://trac.macports.org/ticket/69805

finance/bitcoin/Portfile

@@ -23,6 +23,9 @@ long_description        Bitcoin is a peer-to-peer digital currency. By peer-to-p
                         tasks are managed collectively by the Bitcoin protocol \
                         operating through the nodes of the network.
 
+# https://trac.macports.org/ticket/69805
+platforms               {darwin >= 19}
+
 homepage                https://bitcoincore.org/
 master_sites            ${homepage}bin/bitcoin-core-${version}/
 
@@ -33,7 +36,7 @@ checksums               rmd160  eff46f6cc320cb8f077a9a697fa124ca501abde4 \
 depends_build           port:autoconf \
                         port:automake \
                         port:libtool \
-                        port:pkgconfig \
+                        path:bin/pkg-config:pkgconfig \
                         port:python312
 
 depends_lib             port:libevent \