Fix/unify SBType comparison

Fix/unify SBType comparison

Summary:
In my next step at cleaning up modify-python-lldb.py, I started focusing
on equality comparison. To my surprise, I found out that both python and
c++ versions of the SBType class implement equality comparison, but each
one does it differently. While the python version was implemented in
terms of type name equality, the C++ one used a deep comparison on the
underlying objects.

Removing the python version caused one test to fail (TestTypeList). This
happened because the c++ version of operator== boiled down to
TypePair::operator==, which contains two items: the compiler_type and
type_sp. In this case, the compiler_type was identical, but one of the
objects had the type_sp field unset.

I tried fixing the code so that both objects keep their type_sp member,
but it wasn't easy, because there are so many operations which just work
with the CompilerType types, and so any operation on the SBType (the
test in question was doing GetPointeeType on the type of one variable
and expecting it to match the type of another variable), cause that
second member to be lost.

So instead, here I relax the equality comparison on the TypePair
class. Now, this class ignores the type_sp for the purposes of
comparison, and uses the CompilerType only. This seems reasonable, as
each TypeSP is able to convert itself to a CompilerType.

Reviewers: clayborg, aprantl, serge-sans-paille

Subscribers: jdoerfert, lldb-commits

Differential Revision: https://reviews.llvm.org/D59217

llvm-svn: 356048