bswap is not a library function; use __builtin_bswap[bit-suffix] instead

Author: tautschnig

src/ansi-c/expr2c.cpp

@@ -3532,7 +3532,11 @@ std::string expr2ct::convert_with_precedence(
     return convert_function(src, "isinf", precedence=16);
 
   else if(src.id()==ID_bswap)
-    return convert_function(src, "bswap", precedence=16);
+    return convert_function(
+      src,
+      "__builtin_bswap"+
+      integer2string(pointer_offset_bits(src.op0().type(), ns)),
+      precedence=16);
 
   else if(src.id()==ID_isnormal)
     return convert_function(src, "isnormal", precedence=16);