XaccQuantum: Fix broken ccx (Toffoli)

[ausbin]

The current handling of ccx has two problems in HEAD:

1. It is defined with two qubit operands instead of three
2. The implementation in XaccQuantum attempts to create an XACC instruction that does not exist

Problem 1 manifests as this assertion tripped inside QIR-EE:

$ build/bin/qir-xacc -i test/data/bell_ccx.ll --accelerator qpp
terminate called after throwing an instance of 'qiree::RuntimeError'
  what():  /home/austin/Documents/school/gatech/grad/qsvt/qiree/src/qiree/detail/FunctionChecker.hh:116:
qir-ee: runtime error: arg_size == irfunc_.arg_size() failed:
    incorrect QIR binding supplied: '__quantum__qis__ccx__body' has 3 arguments but QIR-EE expected 2
Aborted

Problem 2 pops up when XACC throws the following exception:

$ build/bin/qir-xacc -i test/data/bell_ccx.ll --accelerator qpp
terminate called after throwing an instance of 'std::runtime_error'
  what():  Invalid instruction name - CCX
Aborted

This commit fixes both issues.