fix build error for unix (#4414)

diff --git a/tools/setup_helpers/ninja_builder.py b/tools/setup_helpers/ninja_builder.py
index b25e609..73b4512 100644
--- a/tools/setup_helpers/ninja_builder.py
+++ b/tools/setup_helpers/ninja_builder.py
@@ -73,6 +73,7 @@
             orig_link = orig_compiler.link
             orig_spawn = orig_compiler.spawn
         else:
+            import distutils.unixccompiler
             orig_compiler = distutils.unixccompiler.UnixCCompiler
             orig_compile = orig_compiler._compile
             orig_link = orig_compiler.link