For disassembly when adding a symbolic operand that is a C++

For disassembly when adding a symbolic operand that is a C++
symbol name, also put the human readable name in a comment.

Also fix a bug in LLVMDisasmInstruction() that was not flushing
the raw_svector_ostream for the disassembled instruction string
before copying it to the output buffer that was causing truncation
of the output.

rdar://10173828

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198441 91177308-0d34-0410-b5e6-96231b3b80d8