MSVC: Fix CMAKE_CL_64 in CXX-only projects (#13896)

When CXX is enabled without C then MSVC_CXX_ARCHITECTURE_ID is set
instead but not MSVC_C_ARCHITECTURE_ID.  Test both.
Merge topic 'CMAKE_CL_64-CXX' into next

fe664b5 MSVC: Fix CMAKE_CL_64 in CXX-only projects (#13896)