ARMClang: Fix typo in -Xlinker flag

Fix a typo from commit ef816610be (ARMClang: allow fallback to -march
and correct setting of --cpu flags, 2020-06-03, v3.18.0-rc1~18^2).

Modules/Compiler/ARMClang.cmake

@@ -61,7 +61,7 @@ function(__armlink_set_cpu_list lang out_var)
   if(__CMAKE_ARMClang_USING_armlink)
     set(__linker_wrapper_flags "")
   else()
-    set(__linker_wrapper_flags --target=${CMAKE_${lang}_COMPILER_TARGET} -XLinker)
+    set(__linker_wrapper_flags --target=${CMAKE_${lang}_COMPILER_TARGET} -Xlinker)
   endif()
 
   execute_process(COMMAND "${CMAKE_LINKER}" ${__linker_wrapper_flags} --cpu=list