When implicitly declaring operators new, new[], delete, and delete[],

give them the appropriate exception specifications. This,
unfortunately, requires us to maintain and/or implicitly generate
handles to namespace "std" and the class "std::bad_alloc". However,
every other approach I've come up with was more hackish, and this
standard requirement itself is quite the hack.

Fixes PR4829.

llvm-svn: 81939