update_test_checks: recognize %if in RUN line

Author: ElvinaYakubova

llvm/utils/update_test_checks.py

@@ -123,7 +123,13 @@ def main():
                 common.warn("Skipping unparsable RUN line: " + l)
                 continue
 
-            commands = [cmd.strip() for cmd in l.split("|")]
+            cropped_content = l
+            if "%if" in l:
+                match = re.search(r'%{\s*(.*?)\s*%}', l)
+                if match:
+                    cropped_content = match.group(1)
+
+            commands = [cmd.strip() for cmd in cropped_content.split("|")]
             assert len(commands) >= 2
             preprocess_cmd = None
             if len(commands) > 2: