Bug#43461: invalid comparison with string literal in default.c

Don't compare string literals as it results in unspecified behavior.

mysys/default.c:
  Test for a empty string.

mysys/default.c

@@ -1083,7 +1083,7 @@ static const char **init_default_directories(MEM_ROOT *alloc)
   if ((env= getenv("ETC")))
     errors += add_directory(alloc, env, dirs);
 #elif defined(DEFAULT_SYSCONFDIR)
-  if (DEFAULT_SYSCONFDIR != "")
+  if (DEFAULT_SYSCONFDIR[0])
     errors += add_directory(alloc, DEFAULT_SYSCONFDIR, dirs);
 #endif /* __EMX__ || __OS2__ */
 

mysys/my_new.cc

@@ -46,8 +46,9 @@ void operator delete[] (void *ptr) throw ()
 
 C_MODE_START
 
-int __cxa_pure_virtual() {
-  assert("Pure virtual method called." == "Aborted");
+int __cxa_pure_virtual()
+{
+  assert(! "Aborted: pure virtual method called.");
   return 0;
 }
 

sql/sql_class.cc

@@ -1758,7 +1758,7 @@ void Query_arena::set_query_arena(Query_arena *set)
 
 void Query_arena::cleanup_stmt()
 {
-  DBUG_ASSERT("Query_arena::cleanup_stmt()" == "not implemented");
+  DBUG_ASSERT(! "Query_arena::cleanup_stmt() not implemented");
 }
 
 /*