Replace $<CONFIG> in IMPORTED_LOCATION

Users might define an OUTPUT_DIRECTORY containing $<CONFIG>.
Copying the byproducts works fine, but for
the imported location we need to replace
the genex. This is possible, since in
single config mode we know the config,
and in multi config mode we know the
config for the `_CONFIG` variants of IMPORTED_LOCATION.

cmake/Corrosion.cmake

@@ -186,8 +186,17 @@ function(_corrosion_set_imported_location_deferred target_name base_property out
         else()
             set(curr_out_dir "${CMAKE_CURRENT_BINARY_DIR}")
         endif()
+        string(REPLACE "\$<CONFIG>" "${config_type}" curr_out_dir "${curr_out_dir}")
         message(DEBUG "Setting ${base_property}_${config_type_upper} for target ${target_name}"
                 " to `${curr_out_dir}/${filename}`.")
+
+        string(GENEX_STRIP "${curr_out_dir}" stripped_out_dir)
+        if(NOT ("${stripped_out_dir}" STREQUAL "${curr_out_dir}"))
+            message(FATAL_ERROR "${output_directory_property} for target ${output_dir_prop_target_name} "
+                    "contained an unexpected Generator expression. Output dir: `${curr_out_dir}`"
+                "Note: Corrosion only supports the `\$<CONFIG>` generator expression for output directories.")
+        endif()
+
         # For Multiconfig we want to specify the correct location for each configuration
         set_property(
             TARGET ${target_name}
@@ -203,6 +212,13 @@ function(_corrosion_set_imported_location_deferred target_name base_property out
         else()
             set(base_output_directory "${CMAKE_CURRENT_BINARY_DIR}")
         endif()
+        string(REPLACE "\$<CONFIG>" "${CMAKE_BUILD_TYPE}" base_output_directory "${base_output_directory}")
+        string(GENEX_STRIP "${base_output_directory}" stripped_out_dir)
+        if(NOT ("${stripped_out_dir}" STREQUAL "${base_output_directory}"))
+            message(FATAL_ERROR "${output_dir_prop_target_name} for target ${output_dir_prop_target_name} "
+                    "contained an unexpected Generator expression. Output dir: `${base_output_directory}`"
+                    "Note: Corrosion only supports the `\$<CONFIG>` generator expression for output directories.")
+        endif()
     endif()
 
     message(DEBUG "Setting ${base_property} for target ${target_name}"