configure.py: enhance systemlibs config

Allow TF_SYSTEM_LIBS env var to split on spaces or commas.
Write PREFIX and related variables to bazelrc as well.

Signed-off-by: Jason Zaman <jason@perfinion.com>
diff --git a/configure.py b/configure.py
index e9d162f..f0b9fad 100644
--- a/configure.py
+++ b/configure.py
@@ -1401,10 +1401,20 @@
 
 def set_system_libs_flag(environ_cp):
   syslibs = environ_cp.get('TF_SYSTEM_LIBS', '')
-  syslibs = ','.join(sorted(syslibs.split(',')))
   if syslibs and syslibs != '':
+    if ',' in syslibs:
+      syslibs = ','.join(sorted(syslibs.split(',')))
+    else:
+      syslibs = ','.join(sorted(syslibs.split()))
     write_action_env_to_bazelrc('TF_SYSTEM_LIBS', syslibs)
 
+  if 'PREFIX' in environ_cp:
+    write_to_bazelrc('build --define=PREFIX=%s' % environ_cp['PREFIX'])
+  if 'LIBDIR' in environ_cp:
+    write_to_bazelrc('build --define=LIBDIR=%s' % environ_cp['LIBDIR'])
+  if 'INCLUDEDIR' in environ_cp:
+    write_to_bazelrc('build --define=INCLUDEDIR=%s' % environ_cp['INCLUDEDIR'])
+
 
 def set_windows_build_flags(environ_cp):
   """Set Windows specific build options."""