Prevent calls to ReturnValue::Set with pointer-valued types.

Prevent calls to ReturnValue::Set with pointer-valued types.

Currently, this code will compile:
  SomePointer* p = ...;
  ReturnValue r = ...;
  r.Set(p);

What happens is that ReturnValue::Set has no pointer-ish overloads, but
a bool one, and hence C++ will convert the pointer to a bool and use
the Set(bool) overload. In other words, the example above is equivalent
to: r.Set(p ? true : false); Which probably isn't what the author had
in mind. This change adds a Set(void*) overload whose body forces a
compile error, to prevent this from happening inadvertently. The only
use of this indeed turned out to be an error.

(Wait for issue 364025 before submitting.)

BUG=
R=dcarney@chromium.org

Review URL: https://codereview.chromium.org/240013004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21217 ce2b1a6d-e550-0410-aec6-3dcde31c8c00