Initial makefile support for cross-compilation to FreeBSD arm64

Relies on fyne-io/fyne-cross#37

go.sum

@@ -11,8 +11,8 @@ cloud.google.com/go/firestore v1.1.0/go.mod h1:ulACoGHTpvq5r8rxGJ4ddJZBZqakUQqCl
 cloud.google.com/go/pubsub v1.0.1/go.mod h1:R0Gpsv3s54REJCy4fxDixWD93lHJMoZTyQ2kNxGRt3I=
 cloud.google.com/go/storage v1.0.0/go.mod h1:IhtSnM/ZTZV8YYJWCY8RULGVqBDmpoyjwiyrjsg+URw=
 dmitri.shuralyov.com/gpu/mtl v0.0.0-20190408044501-666a987793e9/go.mod h1:H6x//7gZCb22OMCxBHrMx7a5I7Hp++hsVxbQ4BYO7hU=
-fyne.io/fyne/v2 v2.0.1 h1:GlW2AHAt3CK5l/cpr0jPfsxWFgNo751yaLk/v3+v888=
-fyne.io/fyne/v2 v2.0.1/go.mod h1:Q12wKzvdrCct+tkaJcMuTmcyDz4ZDjc6+/llerrFnFc=
+fyne.io/fyne/v2 v2.0.2-0.20210330124424-1dfd83be86de h1:0BIwazuzs6ycxCqbPdVE/Rtn2Tg1ES+H0qZNRiRJMUE=
+fyne.io/fyne/v2 v2.0.2-0.20210330124424-1dfd83be86de/go.mod h1:3+FYmLJVgeb8EvTPJ5YzZeo7LkAq4bbuY3Zrir6xHbg=
 github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
 github.com/BurntSushi/xgb v0.0.0-20160522181843-27f122750802/go.mod h1:IVnqGOEym/WlBOVXweHU+Q+/VP0lqqI8lqeDx9IjBqo=
 github.com/Kodeworks/golang-image-ico v0.0.0-20141118225523-73f0f4cfade9/go.mod h1:7uhhqiBaR4CpN0k9rMjOtjpcfGd6DG2m04zQxKnWQ0I=
@@ -48,15 +48,15 @@ github.com/fredbi/uri v0.0.0-20181227131451-3dcfdacbaaf3/go.mod h1:CzM2G82Q9BDUv
 github.com/fsnotify/fsnotify v1.4.7/go.mod h1:jwhsz4b93w/PPRr/qN1Yymfu8t87LnFCMoQvtojpjFo=
 github.com/fsnotify/fsnotify v1.4.9 h1:hsms1Qyu0jgnwNXIxa+/V/PDsU6CfLf6CNO8H7IWoS4=
 github.com/fsnotify/fsnotify v1.4.9/go.mod h1:znqG4EE+3YCdAaPaxE2ZRY/06pZUdp0tY4IgpuI1SZQ=
-github.com/fyne-io/mobile v0.1.2 h1:0HaXDtOOwyOTn3Umi0uKVCOgJtfX73c6unC4U8i5VZU=
-github.com/fyne-io/mobile v0.1.2/go.mod h1:/kOrWrZB6sasLbEy2JIvr4arEzQTXBTZGb3Y96yWbHY=
+github.com/fyne-io/mobile v0.1.3-0.20210318200029-09e9c4e13a8f h1:rguJ/t99j/6zRSFzsBKlsmmyl+vOvCeTJ+2uTBvuXFI=
+github.com/fyne-io/mobile v0.1.3-0.20210318200029-09e9c4e13a8f/go.mod h1:/kOrWrZB6sasLbEy2JIvr4arEzQTXBTZGb3Y96yWbHY=
 github.com/ghodss/yaml v1.0.0/go.mod h1:4dBDuWmgqj2HViK6kFavaiC9ZROes6MMH2rRYeMEF04=
 github.com/go-gl/gl v0.0.0-20190320180904-bf2b1f2f34d7 h1:SCYMcCJ89LjRGwEa0tRluNRiMjZHalQZrVrvTbPh+qw=
 github.com/go-gl/gl v0.0.0-20190320180904-bf2b1f2f34d7/go.mod h1:482civXOzJJCPzJ4ZOX/pwvXBWSnzD4OKMdH4ClKGbk=
 github.com/go-gl/glfw v0.0.0-20190409004039-e6da0acd62b1 h1:QbL/5oDUmRBzO9/Z7Seo6zf912W/a6Sr4Eu0G/3Jho0=
 github.com/go-gl/glfw v0.0.0-20190409004039-e6da0acd62b1/go.mod h1:vR7hzQXu2zJy9AVAgeJqvqgH9Q5CA+iKCZ2gyEVpxRU=
-github.com/go-gl/glfw/v3.3/glfw v0.0.0-20200625191551-73d3c3675aa3 h1:q521PfSp5/z6/sD9FZZOWj4d1MLmfQW8PkRnI9M6PCE=
-github.com/go-gl/glfw/v3.3/glfw v0.0.0-20200625191551-73d3c3675aa3/go.mod h1:tQ2UAYgL5IevRw8kRxooKSPJfGvJ9fJQFa0TUsXzTg8=
+github.com/go-gl/glfw/v3.3/glfw v0.0.0-20210311203641-62640a716d48 h1:QrUfZrT8n72FUuiABt4tbu8PwDnOPAbnj3Mql1UhdRI=
+github.com/go-gl/glfw/v3.3/glfw v0.0.0-20210311203641-62640a716d48/go.mod h1:tQ2UAYgL5IevRw8kRxooKSPJfGvJ9fJQFa0TUsXzTg8=
 github.com/go-kit/kit v0.8.0/go.mod h1:xBxKIO96dXMWWy0MnWVtmwkA9/13aqxPnvrjFYMA2as=
 github.com/go-logfmt/logfmt v0.3.0/go.mod h1:Qt1PoO58o5twSAckw1HlFXLmHsOX5/0LbT9GBnD5lWE=
 github.com/go-logfmt/logfmt v0.4.0/go.mod h1:3RMwSq7FuexP4Kalkev3ejPJsZTpXXBr9+V4qmtdjCk=