Amend two tests that explicitly target C++98

These were previously broken on g++-6 and above, as the compiler defaults to C++14 mode.

Author: smowton

regression/cpp/auto2/test.desc

@@ -1,6 +1,6 @@
 CORE
 main.cpp
-
+-std=c++98
 ^EXIT=0$
 ^SIGNAL=0$
 --

regression/cpp/auto3/test.desc

@@ -1,6 +1,6 @@
 CORE
 main.cpp
-
+-std=c++98
 ^EXIT=(64|1)$
 ^SIGNAL=0$
 parse error