macOS cross compiling fixes

- can't use the x86_64 one as host triplet on arm64 because building Qt
  fails for whatever reason. Because of course it does :D
- vcpkg doesn't always like periods in triplet names so removed those

cmake/ConfigureVcpkg.cmake

@@ -37,10 +37,10 @@ if (USE_RECOMMENDED_TRIPLETS)
         endif()
 
         if (CMAKE_OSX_ARCHITECTURES STREQUAL arm64)
-            set(_WANTED_TRIPLET arm64-osx-11.0-release)
+            set(_WANTED_TRIPLET arm64-osx-11-release)
             set(CMAKE_OSX_DEPLOYMENT_TARGET 11.0)
         else()
-            set(_WANTED_TRIPLET x64-osx-10.15-release)
+            set(_WANTED_TRIPLET x64-osx-1015-release)
             set(CMAKE_OSX_DEPLOYMENT_TARGET 10.15)
         endif()
     elseif(WIN32)
@@ -57,10 +57,18 @@ if (USE_RECOMMENDED_TRIPLETS)
     endif()
 
     if (APPLE)
-        if (_HOST_PROCESSOR STREQUAL arm64 AND _WANTED_TRIPLET MATCHES "-osx")
-            set(_CAN_TARGET_AS_HOST ON)
-        elseif (_WANTED_TRIPLET MATCHES "^x64-osx")
-            set(_CAN_TARGET_AS_HOST ON)
+        if (_HOST_PROCESSOR MATCHES arm64)
+            if (_WANTED_TRIPLET MATCHES "^arm64-osx-")
+                set(_CAN_TARGET_AS_HOST ON)
+            elseif (_WANTED_TRIPLET STREQUAL "x64-osx-1015-release")
+                # Use the default triplet for when building for arm64
+                # because we're probably making a universal build
+                set(VCPKG_HOST_TRIPLET arm64-osx-11-release)
+            endif()
+        else()
+            if (_WANTED_TRIPLET MATCHES "^x64-osx-")
+                set(_CAN_TARGET_AS_HOST ON)
+            endif()
         endif()
     endif()