[mlir][cmake] Fix mlir target export (#153341)

In #152195, target export was
accidentally moved inside a conditional, but it should have been left
outside. This patch undoes that change.

Author: brnorris03

mlir/cmake/modules/AddMLIR.cmake

@@ -641,8 +641,8 @@ function(add_mlir_library_install name)
                               COMPONENT ${name})
     endif()
     set_property(GLOBAL APPEND PROPERTY MLIR_ALL_LIBS ${name})
-    set_property(GLOBAL APPEND PROPERTY MLIR_EXPORTS ${name})
   endif()
+  set_property(GLOBAL APPEND PROPERTY MLIR_EXPORTS ${name})
 endfunction()
 
 # Declare an mlir library which is part of the public C-API.