CTest: Avoid invoking external tool to get the host name

Populate the SITE cache entry using an internal query instead.

Modules/CTest.cmake

@@ -194,7 +194,14 @@ if(BUILD_TESTING)
     "Extra command line flags to pass to the coverage tool")
 
   # set the site name
-  site_name(SITE)
+  if(COMMAND cmake_host_system_information)
+    cmake_host_system_information(RESULT _ctest_hostname QUERY HOSTNAME)
+    set(SITE "${_ctest_hostname}" CACHE STRING "Name of the computer/site where compile is being run")
+    unset(_ctest_hostname)
+  else()
+    # This code path is needed for CMake itself during bootstrap.
+    site_name(SITE)
+  endif()
   # set the build name
   if(NOT BUILDNAME)
     set(DART_COMPILER "${CMAKE_CXX_COMPILER}")