distutils: add build root to libdirs when building uninstalled

The distutils test suite builds extensions which need to link
to libpython despite it being uninstalled. The code currently assumes
that the working directory is the build root, but that is not the case
in the tests (it's in some temp dir). Explicitely pass the build root
instead where the uninstalled libpython can be found.

Lib/distutils/command/build_ext.py

@@ -227,7 +227,7 @@ def finalize_options(self):
                                                       config_dir_name))
             else:
                 # building python standard extensions
-                self.library_dirs.append('.')
+                self.library_dirs.append(sysconfig.project_base)
 
         # For building extensions with a shared Python library,
         # Python's library directory must be appended to library_dirs
@@ -238,7 +238,7 @@ def finalize_options(self):
                 self.library_dirs.append(sysconfig.get_config_var('LIBDIR'))
             else:
                 # building python standard extensions
-                self.library_dirs.append('.')
+                self.library_dirs.append(sysconfig.project_base)
 
         # The argument parsing will result in self.define being a string, but
         # it has to be a list of 2-tuples.  All the preprocessor symbols