[SAoC] MLIR Support for LDC

[Roberto Rosmaninho]

Hi everyone, here goes another update from my project!

This week I was able to build the support for more BinOps:
  - ModExp
  - AndExp
  - OrExp
  - XorExp
  - EqualExp
  - CmpExp(slt,sle,sgt,sge,ult,ule,ugt,uge,neq,eq)

And the last three days I worked to implement Ifstatement witch 
cost me a lot of time to figure out the right way to do that due 
the lack of documentation of implementation (like a doxygen) and 
none examples provided by MLIR. The next week I plan to finish 
those BinOps, replace the opaque BinOps for those provided by a 
StandardDialect from MLIR and start to build the D Dialect. My 
primary goal for now it will be build the ForStatement support so 
we will be able to have some cool tests like matrix 
multiplication or some like that to put on D test suit.

Hopefully next week I'll bring this test to show you, but for now 
you can track my work on 
https://github.com/Robertorosmaninho/ldc/tree/fix-llvm-10 and 
maybe provide some ideas or show me something that I'm not doing 
right.

About the cmake problem on FindMLIR.cmake the one way that I 
could think about solve was passing the MLIR path as cmake 
argument with -DMLIR_ROOT_DIR=/path/to/dir and then all the 
directories necessaries for MLIR works will be set.

Best regards,
Roberto Rosmaninho