Each of the directories,

 /usr/src/servers/pm and    
 /usr/src/servers/vfs 

has its own version of a header file:

 glo.h

In the header file included by all files in the pm directory:

pm.h 

a number of includes are for headers used by all processes and in the standard include directory /usr/src/include

From /usr/src/include 

  #define _POSIX_SOURCE 1
  #define _MINIX 1
  #define _SYSTEM
  #include <minix/config.h>
  #include <ansi.h>
  #include <sys/types.h>
  #include <minix/const.h>
  ...

Then there are additional includes that come from /usr/src/servers/pm, the same directory in which pm.h lives:

  #include "const.h"
  #include "type.h"
  #include "proto.h"
  #include "glo.h"

All files linked into the pm executable include pm.h and so indirectly include the "glo.h" that lives in the pm's directory.