c++/contracts: ICE in C++ Contracts with '-fno-exceptions' [PR 110159]

c++/contracts: ICE in C++ Contracts with '-fno-exceptions' [PR 110159]

We currently only initialise terminate_fn if exceptions are enabled.
However, contract handling requires terminate_fn when building the
contract because a contract failure may result in std::terminate call
regardless of whether the exceptions are enabled. Refactored
init_exception_processing to extract the initialisation of
terminate_fn. New function init_terminate_fn added that initialises
terminate_fn if it hasn't already been initialised. Call to terminate_fn
added in cxx_init_decl_processing if contracts are enabled.

	PR c++/110159

gcc/cp/ChangeLog:

	* cp-tree.h (init_terminate_fn): Declaration of a new function.
	* decl.cc (cxx_init_decl_processing): If contracts are enabled,
	call init_terminate_fn.
	* except.cc (init_exception_processing): Function refactored to
	call init_terminate_fn.
	(init_terminate_fn): Added new function that initializes
	terminate_fn if	it hasn't already been initialised.

gcc/testsuite/ChangeLog:

	* g++.dg/contracts/pr110159.C: New test.

Signed-off-by: Nina Ranns <dinka.ranns@gmail.com>