setup.py: don't prepend the system library directories when building …

…extensions

For some reason the code assumes that relative paths are build paths prepends
the system dirs after relative paths in the existing list. We only uses absolute
paths though, and I don't understand why it even tries to do that.

So just append the system dirs instead.

This fixes the build trying to link against the system Python DLL in case it happens
to be installed.

setup.py

@@ -889,10 +889,8 @@ def init_inc_lib_dirs(self):
             # (PYTHONFRAMEWORK is set) to avoid # linking problems when
             # building a framework with different architectures than
             # the one that is currently installed (issue #7473)
-            add_dir_to_list(self.compiler.library_dirs,
-                            sysconfig.get_config_var("LIBDIR"))
-            add_dir_to_list(self.compiler.include_dirs,
-                            sysconfig.get_config_var("INCLUDEDIR"))
+            self.compiler.library_dirs.append(sysconfig.get_config_var("LIBDIR"))
+            self.compiler.include_dirs.append(sysconfig.get_config_var("INCLUDEDIR"))
 
         system_lib_dirs = ['/lib64', '/usr/lib64', '/lib', '/usr/lib']
         system_include_dirs = ['/usr/include']