build: support for mips64el

Built and tested successfully on Loongson 3A2000
with Fedora25(mips64el distribution).

PR-URL: #10991
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>

configure

@@ -711,6 +711,9 @@ def host_arch_cc():
       if rtn != 's390':
         break
 
+  if rtn == 'mipsel' and '_LP64' in k:
+    rtn = 'mips64el'
+
   return rtn
 
 
@@ -792,7 +795,7 @@ def configure_node(o):
 
   if target_arch == 'arm':
     configure_arm(o)
-  elif target_arch in ('mips', 'mipsel'):
+  elif target_arch in ('mips', 'mipsel', 'mips64el'):
     configure_mips(o)
 
   if flavor == 'aix':