filesystem: wscript: add dummy filesystem_includes target that only exposes public filesystem_stdio include paths

filesystem/wscript

@@ -15,10 +15,10 @@ def configure(conf):
 			conf.env.cxxshlib_PATTERN = conf.env.cxxshlib_PATTERN[3:]
 
 def build(bld):
+	bld(name = 'filesystem_includes', export_includes = '.')
 	bld.shlib(target = 'filesystem_stdio',
 		features = 'cxx',
 		source = bld.path.ant_glob(['*.c', '*.cpp']),
-		includes = ['.', '../common', '../public', '../engine'],
+		use = 'filesystem_includes public',
-		use = ['public'],
 		install_path = bld.env.LIBDIR,
 		subsystem = bld.env.MSVC_SUBSYSTEM)