The toolchain will already search these locations by default if appropriate,
but /usr/lib isn't right on a 64-bit system where native objects are in /usr/lib64
and /usr/lib has multilib 32-bit ones. bfd warns on this but lld rejects it.

https://bugs.gentoo.org/946846
--- a/setup.py
+++ b/setup.py
@@ -84,12 +84,6 @@ if os.environ.get("READTHEDOCS", None) is None:
             )
         )
 
-    # add standard locs
-    incdir_list.append("/usr/local/include")
-    libdir_list.append("/usr/local/lib")
-    incdir_list.append("/usr/include")
-    libdir_list.append("/usr/lib")
-
     # build the librsync extension
     ext_modules = [
         Extension(