Enable building on GNU/Hurd platforms

Author: ellert

CHANGELOG.rst

@@ -12,6 +12,7 @@ version develop
 -----------------
 + Use upstream ISA-L version 2.31.1 which includes patches to make 
   installation possible.
++ Enable building on GNU/Hurd platforms.
 
 version 1.7.1
 -----------------

setup.py

@@ -26,6 +26,7 @@
                  sys.platform.startswith("netbsd"))
 SYSTEM_IS_UNIX = (sys.platform.startswith("linux") or
                   sys.platform.startswith("darwin") or
+                  sys.platform.startswith("gnu") or
                   SYSTEM_IS_BSD)
 SYSTEM_IS_WINDOWS = sys.platform.startswith("win")