compilers/d: Add missing method for dmd and ldc

This allows coverage to be generated, although we can't yet do anything
useful with it.

mesonbuild/compilers/d.py

@@ -105,6 +105,9 @@ class DmdLikeCompilerMixin:
     def get_coverage_args(self):
         return ['-cov']
 
+    def get_coverage_link_args(self):
+        return []
+
     def get_preprocess_only_args(self):
         return ['-E']