Fix #12396 FP nullPointer for pthread_create with function type cast (#5927)

Author: chrchr-github

lib/valueflow.cpp

@@ -7863,7 +7863,7 @@ static void setFunctionReturnValue(const Function* f, Token* tok, ValueFlow::Val
 static void valueFlowFunctionReturn(TokenList &tokenlist, ErrorLogger *errorLogger, const Settings& settings)
 {
     for (Token *tok = tokenlist.back(); tok; tok = tok->previous()) {
-        if (tok->str() != "(" || !tok->astOperand1())
+        if (tok->str() != "(" || !tok->astOperand1() || tok->isCast())
             continue;
 
         const Function* function = nullptr;

test/cfg/posix.c

@@ -1023,6 +1023,17 @@ void nullPointer(char *p, int fd, pthread_mutex_t mutex)
     pthread_mutex_unlock(NULL);
 }
 
+void* f_returns_NULL(void* arg)
+{
+    return NULL;
+}
+
+void nullPointer_pthread_create() // #12396
+{
+    pthread_t thread;
+    pthread_create(&thread, NULL, (void* (*)(void*))f_returns_NULL, NULL);
+}
+
 void memleak_getaddrinfo()
 {
     //TODO: nothing to report yet, see http://sourceforge.net/p/cppcheck/discussion/general/thread/d9737d5d/