fix issue 12520 - allow comparison of empty tuples to tuples that con…

[ghost]

…tain values

Empty tuples are represented as TypeTuple while tuples containing values as TupleExp.
As a consequence, comparing them using == was not allowed.

[dlang-bot]

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	12520	normal	Comparing two TypeTuples with == does not compile for no arguments

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "stable + dmd#11187"