Change the mangling of a ref-qualifier on a function type so that

Change the mangling of a ref-qualifier on a function type so that
it is placed in a position which is never ambiguous with a
reference-to-function type.  This follows some recent discussion
and ensuing proposal on cxx-abi-dev.  It is not necessary to
change the mangling of CV-qualifiers because you cannot
apply CV-qualification in the normal sense to a function type.
It is not necessary to change the mangling of ref-qualifiers on
method declarations because they appear in an unambiguous
location.

In addition, mangle CV-qualifiers and ref-qualifiers on function
types when they occur in positions other than member pointers
(that is, when they appear as template arguments).

This is a minor ABI break with previous releases of clang.  It
is not considered critical because (1) ref-qualifiers are
relatively rare, since AFAIK we're the only implementing compiler,
and (2) they're particularly likely to come up in contexts that
do not rely on the ODR for correctness.  We apologize for any
inconvenience;  this is the right thing to do.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@156794 91177308-0d34-0410-b5e6-96231b3b80d8