enabled and mitigated -Wunreachable-code Clang warnings (#4818)

Author: firewave

cmake/compileroptions.cmake

@@ -91,7 +91,6 @@ elseif (CMAKE_CXX_COMPILER_ID MATCHES "Clang")
    add_compile_options_safe(-Wno-double-promotion)
    add_compile_options_safe(-Wno-shadow-field)
    add_compile_options_safe(-Wno-shadow-uncaptured-local)
-   add_compile_options_safe(-Wno-unreachable-code)
    add_compile_options_safe(-Wno-implicit-float-conversion)
    add_compile_options_safe(-Wno-switch-enum)
    add_compile_options_safe(-Wno-float-conversion)

lib/checkclass.cpp

@@ -2857,10 +2857,8 @@ void CheckClass::checkCopyCtorAndEqOperator()
 {
     // This is disabled because of #8388
     // The message must be clarified. How is the behaviour different?
-    return;
-
     // cppcheck-suppress unreachableCode - remove when code is enabled again
-    if (!mSettings->severity.isEnabled(Severity::warning))
+    if ((true) || !mSettings->severity.isEnabled(Severity::warning))
         return;
 
     for (const Scope * scope : mSymbolDatabase->classAndStructScopes) {

lib/symboldatabase.cpp

@@ -1747,7 +1747,7 @@ bool SymbolDatabase::isFunction(const Token *tok, const Scope* outerScope, const
     // function returning function pointer? '... ( ... %name% ( ... ))( ... ) {'
     // function returning reference to array '... ( & %name% ( ... ))[ ... ] {'
     // TODO: Activate this again
-    if (false && tok->str() == "(" && tok->strAt(1) != "*" &&
+    if ((false) && tok->str() == "(" && tok->strAt(1) != "*" &&
         (tok->link()->previous()->str() == ")" || Token::simpleMatch(tok->link()->tokAt(-2), ") const"))) {
         const Token* tok2 = tok->link()->next();
         if (tok2 && tok2->str() == "(" && Token::Match(tok2->link()->next(), "{|;|const|=")) {