CMakeSystem: include toolchain file after setting CMAKE_HOST_ (#13796)

Make the CMAKE_HOST_* variables always available in the toolchain file.
They are when the file is included in CMakeDetermineSystem.cmake, and
now also here.  For the non-cross-compiling case this does not change
anything at all.

Alex

Modules/CMakeSystem.cmake.in

@@ -1,3 +1,8 @@
+set(CMAKE_HOST_SYSTEM "@CMAKE_HOST_SYSTEM@")
+set(CMAKE_HOST_SYSTEM_NAME "@CMAKE_HOST_SYSTEM_NAME@")
+set(CMAKE_HOST_SYSTEM_VERSION "@CMAKE_HOST_SYSTEM_VERSION@")
+set(CMAKE_HOST_SYSTEM_PROCESSOR "@CMAKE_HOST_SYSTEM_PROCESSOR@")
+
 @INCLUDE_CMAKE_TOOLCHAIN_FILE_IF_REQUIRED@
 
 set(CMAKE_SYSTEM "@CMAKE_SYSTEM@")
@@ -5,11 +10,6 @@ set(CMAKE_SYSTEM_NAME "@CMAKE_SYSTEM_NAME@")
 set(CMAKE_SYSTEM_VERSION "@CMAKE_SYSTEM_VERSION@")
 set(CMAKE_SYSTEM_PROCESSOR "@CMAKE_SYSTEM_PROCESSOR@")
 
-set(CMAKE_HOST_SYSTEM "@CMAKE_HOST_SYSTEM@")
-set(CMAKE_HOST_SYSTEM_NAME "@CMAKE_HOST_SYSTEM_NAME@")
-set(CMAKE_HOST_SYSTEM_VERSION "@CMAKE_HOST_SYSTEM_VERSION@")
-set(CMAKE_HOST_SYSTEM_PROCESSOR "@CMAKE_HOST_SYSTEM_PROCESSOR@")
-
 set(CMAKE_CROSSCOMPILING "@CMAKE_CROSSCOMPILING@")
 
 set(CMAKE_SYSTEM_LOADED 1)