Track our dependencies' main branches.

This also requires a maccore bump.

Diff: d2ef9d7ee0..424fa26148

.gitmodules

@@ -1,19 +1,20 @@
 [submodule "external/guiunit"]
     path = external/guiunit
     url = ../../mono/guiunit.git
+    branch = main
 [submodule "external/macios-binaries"]
     path = external/macios-binaries
     url = ../../xamarin/macios-binaries
-    branch = master
+    branch = main
 [submodule "external/opentk"]
     path = external/opentk
     url = ../../mono/opentk.git
-    branch = master
+    branch = main
 [submodule "external/Touch.Unit"]
     path = external/Touch.Unit
     url = ../../spouliot/Touch.Unit.git
-    branch = master
+    branch = main
 [submodule "external/Xamarin.MacDev"]
     path = external/Xamarin.MacDev
     url = ../../xamarin/Xamarin.MacDev
-    branch = master
+    branch = main

mk/xamarin.mk

@@ -7,8 +7,8 @@ MONO_BRANCH    := $(shell cd $(MONO_PATH) 2> /dev/null && git symbolic-ref --sho
 endif
 
 ifdef ENABLE_XAMARIN
-NEEDED_MACCORE_VERSION := d2ef9d7ee008e1a07a29396c68df33cc4f02de18
-NEEDED_MACCORE_BRANCH := master
+NEEDED_MACCORE_VERSION := 424fa2614873c7415cf0407d2389335cba0b6c79
+NEEDED_MACCORE_BRANCH := main
 
 MACCORE_DIRECTORY := maccore
 MACCORE_MODULE    := git@github.com:xamarin/maccore.git