FindMatlab: Avoid if() auto-dereference in 64-bit host detection

If the value of `CMAKE_HOST_SYSTEM_PROCESSOR` also happens to be set as
a variable by a project (e.g. `AMD64`), allowing `if()` to
auto-dereference is unlikely to produce a value that matches "64".
Instead let `if()` auto-dereference `CMAKE_HOST_SYSTEM_PROCESSOR`.

Fixes: #17460

Modules/FindMatlab.cmake

@@ -356,7 +356,7 @@ function(matlab_extract_all_installed_versions_from_registry win64 matlab_versio
   endif()
 
 
-  if(${win64} AND ${CMAKE_HOST_SYSTEM_PROCESSOR} MATCHES "64")
+  if(${win64} AND CMAKE_HOST_SYSTEM_PROCESSOR MATCHES "64")
     set(APPEND_REG "/reg:64")
   else()
     set(APPEND_REG "/reg:32")