Internals: Improve cppcheck flow and fix up issues (#6311)

Added cppcheck-suppressions.txt in the repo root. You can add new
patterns in there instead of having to parse the XML output.

Also configure to add the -D__GNUC__ preprocessor macro, which makes it
understand UASSERT (it understands the 'noreturn' function attribute).

Added some case by case specific suppressions and fixed up other code,
especially in V3Ast*h and V3Dfg*.h, including code generated by astgen
that had some no-ops that irks cppcheck.

One thing it does not seem to like is `const` class members with default
initializers in the class. It will assume that's always the value, even
if overridden in the constructor. We had few so removed them.

With that a lot of files in `src/` are now clean or only have a handful
of issues. Therefore, I have also deleted cppcheck_filtered, and made it
produce human readable output straight to the terminal.

Regarding cleaning up the reported nits, I kind of got bored after
V3[A-E] so pausing here. Apologies for the merge conflicts.

Tested with cppcheck 2.13.0

src/V3Control.h

@@ -51,7 +51,8 @@ public:
     static void applyFTask(AstNodeModule* modulep, AstNodeFTask* ftaskp);
     static void applyIgnores(FileLine* filelinep);
     static void applyModule(AstNodeModule* modulep);
-    static void applyVarAttr(AstNodeModule* modulep, AstNodeFTask* ftaskp, AstVar* varp);
+    static void applyVarAttr(const AstNodeModule* modulep, const AstNodeFTask* ftaskp,
+                             AstVar* varp);
 
     static int getHierWorkers(const string& model);
     static FileLine* getHierWorkersFileLine(const string& model);
@@ -64,7 +65,7 @@ public:
 
     static bool containsMTaskProfileData();
 
-    static bool waive(FileLine* filelinep, V3ErrorCode code, const string& message);
+    static bool waive(const FileLine* filelinep, V3ErrorCode code, const string& message);
 };
 
 #endif  // Guard