invalid preprocessing directive #extern when using umm_malloc

[andig]

After upgrading

Updating fec1a64..55e5bdf

Including umm_malloc is no longer possible- regardless if called with extern or not:

//extern "C" {
  #include <user_interface.h>
  #include <umm_malloc/umm_malloc.h>
//}

result:

In file included from C:\andi\arduino\hardware\esp8266com\esp8266\cores\esp8266/umm_malloc/umm_malloc.h:13:0,
         from C:\andi\htdocs\vzero\vzero.ino:37:
C:\andi\arduino\hardware\esp8266com\esp8266\cores\esp8266/umm_malloc/umm_malloc_cfg.h:10:2: error: invalid preprocessing directive #extern
 #extern "C" {
  ^
exit status 1
Error compiling.

[andig]

Should it possibly be extern "C" instead of #extern "C" in https://github.com/esp8266/Arduino/blob/master/cores/esp8266/umm_malloc/umm_malloc_cfg.h#L10?