base: common_plugin.h add missing typedefs

ea90ca86664c73fb8d415f3cc7baacdf8a6dd685("Move some infra bits of
lib/krb5/ to lib/base/ (2)") forgot to add typedefs

  heim_get_instance_func_t
  krb5_get_instance_t

required for compilation of krb5_get_instance style plugins.

Change-Id: I3130f86034be1f9f79694eca0d1b309e247fd03f

lib/base/common_plugin.h

@@ -55,6 +55,10 @@
 /* For krb5 plugins, this is a krb5_context */
 typedef struct heim_pcontext_s *heim_pcontext;
 
+typedef uintptr_t
+(HEIM_LIB_CALL *heim_get_instance_func_t)(const char *);
+typedef heim_get_instance_func_t krb5_get_instance_t;
+
 /*
  * All plugin function tables extend the following structure.
  */