When TableGen finds an error in the SparcV9.td file, it exits with a non-zero

exit code. This, in turn, makes an empty file SparcV9CodeEmitter.inc, and only
much later, produces a link error because the key function that TableGen creates
isn't found.

Using a temporary file in the middle forces a good .INC file to be generated by
TableGen, and it will keep trying until you fix the input file.

llvm-svn: 6392