fix build dir

Builds/CMake/deps/Nudb.cmake

@@ -0,0 +1,31 @@
+#[===================================================================[
+   NIH dep: nudb
+
+   NuDB is header-only, thus is an INTERFACE lib in CMake.
+   TODO: move the library definition into NuDB repo and add
+   proper targets and export/install
+#]===================================================================]
+
+if (is_root_project) # NuDB not needed in the case of xrpl_core inclusion build
+  add_library (nudb INTERFACE)
+  FetchContent_Declare(
+    nudb_src
+    GIT_REPOSITORY https://github.com/CPPAlliance/NuDB.git
+    GIT_TAG        2.0.5
+  )
+  FetchContent_GetProperties(nudb_src)
+  if(NOT nudb_src_POPULATED)
+    message (STATUS "Pausing to download NuDB...")
+    FetchContent_Populate(nudb_src)
+  endif()
+
+  file(TO_CMAKE_PATH "${nudb_src_SOURCE_DIR}" nudb_src_SOURCE_DIR)
+  # specify as system includes so as to avoid warnings
+  target_include_directories (nudb SYSTEM INTERFACE ${nudb_src_SOURCE_DIR}/include)
+  target_link_libraries (nudb
+    INTERFACE
+      Boost::thread
+      Boost::system)
+  add_library (NIH::nudb ALIAS nudb)
+  target_link_libraries (ripple_libs INTERFACE NIH::nudb)
+endif ()