Never return null pointer by C++ operator new (gc_cpp)

Never return null pointer by C++ operator new (gc_cpp)

Now, in case of the allocation failure, new and new[] operators throw
bad_alloc (or abort the application if an ancient compiler is used).

* gc_cpp.cc (GC_NEW_DELETE_NEED_THROW): Remove.
* gc_cpp.cc (GC_DECL_NEW_THROW, GC_DECL_DELETE_THROW): Move macro
definition to gc_cpp.h.
* gc_cpp.cc [GC_NEW_DELETE_NEED_THROW]: Do not include "new" header.
* gc_cpp.cc [!_MSC_VER] (operator new): Call GC_OP_NEW_OOM_CHECK() for
the allocation result.
* gc_cpp.cc [!_MSC_VER && GC_OPERATOR_NEW_ARRAY && !CPPCHECK]
(operator new[]): Likewise.
* include/gc.h (GC_abort_on_oom): Declare new API function.
* include/gc_cpp.h [!GC_NEW_DELETE_THROW_NOT_NEEDED
&& (GC_GNUC_PREREQ(4,2) || __BORLANDC__>=0x0550 || _MSC_VER>1020
|| __WATCOMC__>=1050)] (GC_NEW_DELETE_NEED_THROW):
Define macro.
* include/gc_cpp.h [GC_NEW_DELETE_NEED_THROW]: Include "new" header.
* include/gc_cpp.h (GC_OP_NEW_OOM_CHECK): New internal macro (throws
bad_alloc or cals GC_abort_on_oom).
* include/gc_cpp.h (gc::new(size_t), gc::new(size_t,GCPlacement), new):
Add GC_DECL_NEW_THROW; call GC_OP_NEW_OOM_CHECK() for the allocation
result.
* include/gc_cpp.h [GC_OPERATOR_NEW_ARRAY] (gc::new[](size_t),
gc::new[](size_t,GCPlacement, new[]): Likewise.
* misc.c (GC_abort_on_oom): Implement function.
* tests/test.c [CPPCHECK] (main): Call UNTESTED(GC_abort_on_oom).