configure: Add TF_SYSTEM_LIBS handling

tensorflow#20284 Added the framework
to unbundle deps and use system libraries. The TF_SYSTEM_LIBS variable
needed to be added manually. This makes configure handle it for
convenience. There is no prompt yet, that will be added later.

Signed-off-by: Jason Zaman <jason@perfinion.com>

configure.py

@@ -1403,6 +1403,13 @@ def set_build_strip_flag():
   write_to_bazelrc('build --strip=always')
 
 
+def set_system_libs_flag(environ_cp):
+  syslibs = environ_cp.get("TF_SYSTEM_LIBS", "")
+  syslibs = ",".join(sorted(syslibs.split(",")))
+  if syslibs and syslibs != "":
+    write_action_env_to_bazelrc("TF_SYSTEM_LIBS", syslibs)
+
+
 def set_windows_build_flags(environ_cp):
   """Set Windows specific build options."""
   # The non-monolithic build is not supported yet
@@ -1560,6 +1567,7 @@ def main():
   set_grpc_build_flags()
   set_cc_opt_flags(environ_cp)
   set_build_strip_flag()
+  set_system_libs_flag(environ_cp)
   if is_windows():
     set_windows_build_flags(environ_cp)