core: Make PrivilegeHeper::drop|raise no-op operations on platforms that do not support drop/elevation of privileges

Change-Id: I13b53ba27cee59d58b816d060501499517e6dc37
diff --git a/core/privilege-helper.cpp b/core/privilege-helper.cpp
index e8bbf0f..93b7142 100644
--- a/core/privilege-helper.cpp
+++ b/core/privilege-helper.cpp
@@ -159,7 +159,7 @@
 
   NFD_LOG_INFO("dropped to effective uid=" << ::geteuid() << " gid=" << ::getegid());
 #else
-  throw Error("Dropping privileges is not supported on this platform");
+  NFD_LOG_WARN("Dropping privileges is not supported on this platform");
 #endif // HAVE_PRIVILEGE_DROP_AND_ELEVATE
 }
 
@@ -186,7 +186,7 @@
     }
   NFD_LOG_INFO("elevated to effective uid=" << ::geteuid() << " gid=" << ::getegid());
 #else
-  throw Error("Elevating privileges is not supported on this platform");
+  NFD_LOG_WARN("Elevating privileges is not supported on this platform");
 #endif // HAVE_PRIVILEGE_DROP_AND_ELEVATE
 }