[fix] Cppcheck suppress unusedFunction checker only once

Cppcheck 2.17 fails when a checker is suppressed multiple times.
Fixes #4498

Author: bruntib

analyzer/codechecker_analyzer/analyzers/cppcheck/analyzer.py

@@ -219,7 +219,8 @@ def construct_analyzer_cmd(self, result_handler):
 
             # unusedFunction check is for whole program analysis,
             # which is not compatible with per source file analysis.
-            analyzer_cmd.append('--suppress=unusedFunction')
+            if '--suppress=unusedFunction' not in analyzer_cmd:
+                analyzer_cmd.append('--suppress=unusedFunction')
 
             # Add extra arguments.
             analyzer_cmd.extend(config.analyzer_extra_arguments)