Fix setting of CMAKE_SYSTEM_NAME

ios.toolchain.cmake

@@ -724,18 +724,24 @@ endforeach()
 # CMake 3.14+ support building for iOS, watchOS, and tvOS out of the box.
 if(MODERN_CMAKE)
   if(SDK_NAME MATCHES "iphone")
-    set(CMAKE_SYSTEM_NAME iOS)
+    set(TOOLCHAIN_SYSTEM_NAME iOS)
   elseif(SDK_NAME MATCHES "xros")
-      set(CMAKE_SYSTEM_NAME visionOS)
+    set(TOOLCHAIN_SYSTEM_NAME visionOS)
   elseif(SDK_NAME MATCHES "xrsimulator")
-      set(CMAKE_SYSTEM_NAME visionOS)
+    set(TOOLCHAIN_SYSTEM_NAME visionOS)
   elseif(SDK_NAME MATCHES "macosx")
-    set(CMAKE_SYSTEM_NAME Darwin)
+    set(TOOLCHAIN_SYSTEM_NAME Darwin)
   elseif(SDK_NAME MATCHES "appletv")
-    set(CMAKE_SYSTEM_NAME tvOS)
+    set(TOOLCHAIN_SYSTEM_NAME tvOS)
   elseif(SDK_NAME MATCHES "watch")
-    set(CMAKE_SYSTEM_NAME watchOS)
+    set(TOOLCHAIN_SYSTEM_NAME watchOS)
   endif()
+
+  # This is done because simply setting CMAKE_SYSTEM_NAME already enables CMAKE_CROSSCOMPILING, which is undesirable when building on mac for mac.
+  if(NOT ${CMAKE_HOST_SYSTEM_NAME} STREQUAL ${TOOLCHAIN_SYSTEM_NAME})
+    set(CMAKE_SYSTEM_NAME ${TOOLCHAIN_SYSTEM_NAME})
+  endif()
+
   # Provide flags for a combined FAT library build on newer CMake versions
   if(PLATFORM_INT MATCHES ".*COMBINED")
     set(CMAKE_IOS_INSTALL_COMBINED YES)