Cleanup ConstantExpr handling:
* Correctly delete TypeHandles in AsmParser. In addition to not leaking
memory, this prevents a bug that could have occurred when a type got
resolved that the constexpr was using
* Check for errors in the AsmParser instead of hitting assertion failures
deep in the code
* Simplify the interface to the ConstantExpr class, removing unneccesary
parameters to the ::get* methods.
* Rename the 'getelementptr' version of ConstantExpr::get to
ConstantExpr::getGetElementPtr
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@3161
91177308-0d34-0410-b5e6-
96231b3b80d8