"lit"-based test suite

[Johan Engelen via digitalmars-d-ldc]

Hi all,
   I've come to like the "lit"-based test suite a lot. It is much 
easier (for me at least) to run those tests than to run the DMD 
testsuite, especially on Windows.

I propose:
- Move the lit python script from ./tests/ir to ./tests.
- Exclude the "d2" folder from lit testing
- Move the LDC-specific tests from the DMD testsuite into a few 
other ./tests/abc directories and run them with lit instead

A big immediate benefit that I see is that it will be easier to 
add testcases and that testcases can be added in the same 
merge/commit as the implementation/fix for the testcase. (the 
submodule thing is a little annoying)
Also, I think the lit system has more flexibility for testing.

What do you think?

cheers,
   Johan