sanitycheck: support coverage with unit tests

Fix setting coverage for unit tests and link against gcov when coverage
is enabled.

Fixes #24674

Signed-off-by: Anas Nashif <anas.nashif@intel.com>
diff --git a/scripts/sanity_chk/sanitylib.py b/scripts/sanity_chk/sanitylib.py
index 65ccf48..ac5b487 100644
--- a/scripts/sanity_chk/sanitylib.py
+++ b/scripts/sanity_chk/sanitylib.py
@@ -1854,6 +1854,8 @@
         elif instance.testcase.type == "unit":
             instance.handler = BinaryHandler(instance, "unit")
             instance.handler.binary = os.path.join(instance.build_dir, "testbinary")
+            if self.coverage:
+                args.append("COVERAGE=1")
         elif instance.platform.type == "native":
             handler = BinaryHandler(instance, "native")