fix: always use top level build dir for output

Even if the project is used as a sub-project, we want all output artifacts to
be placed in the top level build dir so that we can run tests, collect install
artifacts, etc... from a single location. THis would work if the project is used
as a top-level or as a sub-project.

CMakeLists.txt

@@ -96,9 +96,9 @@ project(
   LANGUAGES C CXX)
 
 # Set output directories
-set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${PROJECT_BINARY_DIR}/bin)
-set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${PROJECT_BINARY_DIR}/bin)
-set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${PROJECT_BINARY_DIR}/lib)
+set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)
+set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)
+set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib)
 
 # Create version file
 file(WRITE "${PROJECT_BINARY_DIR}/VERSION" "${META_NAME_VERSION}")