[llvm] [Hexagon] Enable Machine Combiner pass. (PR #169434)

[Sumanth Gundapaneni via llvm-commits]

sgundapa wrote:

> > This patch will reduce some downstream delta and will be a crucial piece in some of the optimizations
> 
> Is this pass on by default in ~typical optimization levels like -O1/-O2? If so, can you run the llvm-test-suite to check for regressions?

Yes. It is on by default. 

https://github.com/llvm/llvm-project/pull/169434