Add gnu hurd to *_machine information

docs/markdown/Reference-tables.md

@@ -84,6 +84,7 @@ These are provided by the `.system()` method call.
 | freebsd             | FreeBSD and its derivatives |
 | dragonfly           | DragonFly BSD |
 | netbsd              | |
+| gnu                 | GNU Hurd |
 
 Any string not listed above is not guaranteed to remain stable in
 future releases.

test cases/common/137 get define/meson.build

@@ -32,6 +32,9 @@ foreach lang : ['c', 'cpp']
   elif host_system == 'netbsd'
     d = cc.get_define('__NetBSD__')
     assert(d == '1', '__NetBSD__ value is @0@ instead of 1'.format(d))
+  elif host_system == 'gnu'
+    d = cc.get_define('__GNU__')
+    assert(d == '1', '__GNU__ value is @0@ instead of 1'.format(d))
   else
     error('Please report a bug and help us improve support for this platform')
   endif