test: add back clang version check for test_hexagon

Older distros like Ubuntu 18.04 and Debian 10 ship clang < 10 that
dont have hexagon support. The previous commit removed the version
check so the test started failing on those images.

Put the version check inside the skipif decorator instead so we dont
crash during test collection when clang is missing.

Fixes: 79df4a9 ("test: fix test collection failure when clang is not installed")
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>

Author: roxell

test/test_build.py

@@ -467,7 +467,16 @@ def test_arc(self, linux):
         assert "uImage.gz" in [str(f.name) for f in result.output_dir.glob("*")]
 
     @pytest.mark.skipif(shutil.which("ld.lld") is None, reason="requires lld")
-    @pytest.mark.skipif(shutil.which("clang") is None, reason="requires clang")
+    @pytest.mark.skipif(
+        shutil.which("clang") is None
+        or int(
+            subprocess.check_output(["clang", "-dumpversion"], encoding="utf-8").split(
+                "."
+            )[0]
+        )
+        < 10,
+        reason="requires clang 10+",
+    )
     def test_hexagon(self, linux):
         result = build(tree=linux, target_arch="hexagon", toolchain="clang")
         assert result.passed