Avoid "-Wzero-as-null-pointer-constant" warnings on the generated code.

Reported in
<https://lists.gnu.org/archive/html/bug-gnulib/2024-11/msg00123.html>.

* src/output.cc (Output::output_lookup_function_body): To denote a null
pointer, emit a cast expression instead of plain "0".
* tests/c-parse.exp, tests/charsets.exp, tests/chill.exp,
tests/cplusplus.exp, tests/gpc.exp, tests/incomplete.exp,
tests/java.exp, tests/languages.exp, tests/modula2.exp, tests/objc.exp,
tests/permut2.exp, tests/permut3.exp, tests/permutc2.exp,
tests/test-4.exp: Update.

tests/c-parse.exp

@@ -219,5 +219,5 @@ is_reserved_word (str, len)
             return &wordlist[key];
         }
     }
-  return 0;
+  return (struct resword *) 0;
 }

tests/charsets.exp

@@ -1878,6 +1878,6 @@ in_word_set (register const char *str, register size_t len)
             return &wordlist[key];
         }
     }
-  return 0;
+  return (struct charset *) 0;
 }
 

tests/chill.exp

@@ -1550,7 +1550,7 @@ in_word_set (str, len)
                 resword = &wordlist[299];
                 goto compare;
             }
-          return 0;
+          return (struct resword *) 0;
         compare:
           {
             register const char *s = resword->name;
@@ -1560,5 +1560,5 @@ in_word_set (str, len)
           }
         }
     }
-  return 0;
+  return (struct resword *) 0;
 }

tests/cplusplus.exp

@@ -269,5 +269,5 @@ is_reserved_word (str, len)
             return &wordlist[key];
         }
     }
-  return 0;
+  return (struct resword *) 0;
 }

tests/gpc.exp

@@ -153,5 +153,5 @@ is_reserved_word (register const char *str, register size_t len)
             return &wordlist[key];
         }
     }
-  return 0;
+  return (struct resword *) 0;
 }

tests/incomplete.exp

@@ -121,5 +121,5 @@ in_word_set (register const char *str, register size_t len)
             return &wordlist[key];
         }
     }
-  return 0;
+  return (struct month *) 0;
 }

tests/java.exp

@@ -199,5 +199,5 @@ java_keyword (str, len)
             return &wordlist[key];
         }
     }
-  return 0;
+  return (struct java_keyword *) 0;
 }

tests/languages.exp

@@ -1495,7 +1495,7 @@ in_word_set (register const char *str, register size_t len)
             return &wordlist[key];
         }
     }
-  return 0;
+  return (struct language *) 0;
 }
 
 

tests/modula2.exp

@@ -246,5 +246,5 @@ in_word_set (register const char *str, register size_t len)
               return s;
           }
     }
-  return 0;
+  return (const char *) 0;
 }

tests/objc.exp

@@ -194,5 +194,5 @@ is_reserved_word (register const char *str, register size_t len)
             return &wordlist[key];
         }
     }
-  return 0;
+  return (struct resword *) 0;
 }

tests/permut2.exp

@@ -104,5 +104,5 @@ in_word_set (register const char *str, register size_t len)
             return s;
         }
     }
-  return 0;
+  return (const char *) 0;
 }

tests/permut3.exp

@@ -104,5 +104,5 @@ in_word_set (register const char *str, register size_t len)
             return s;
         }
     }
-  return 0;
+  return (const char *) 0;
 }

tests/permutc2.exp

@@ -153,5 +153,5 @@ in_word_set (register const char *str, register size_t len)
             return s;
         }
     }
-  return 0;
+  return (const char *) 0;
 }

tests/test-4.exp

@@ -230,5 +230,5 @@ in_word_set (register const char *str, register size_t len)
             }
         }
     }
-  return 0;
+  return (struct resword *) 0;
 }