Use noexcept specifier in gc_cpp if C++11

Use noexcept specifier in gc_cpp if C++11

* gc_cpp.cc [!_MSC_VER && !__DMC__] (delete, delete[]): Rename
GC_DECL_DELETE_THROW to GC_NOEXCEPT.
* include/gc_cpp.h: Always include "new" header.
* include/gc_cpp.h [!GC_NEW_DELETE_THROW_NOT_NEEDED]
(GC_NEW_DELETE_NEED_THROW): Do not define if __BORLANDC__ or _MSC_VER,
or __WATCOMC__, or if __cplusplus>=201103L and !__clang__.
* include/gc_cpp.h (GC_DECL_DELETE_THROW): Remove.
* include/gc_cpp.h [!GC_NOEXCEPT] (GC_NOEXCEPT): Define internal macro
to except or throw(), or nothing (same as that in gc_allocator.h).
* include/gc_cpp.h [!GC_NEW_ABORTS_ON_OOM] (GC_NEW_ABORTS_ON_OOM):
Define if GC_NOEXCEPT is defined to nothing.
* include/gc_cpp.h (new(size_t,void*), new[](size_t,void*), delete):
Add GC_NOEXCEPT.