[clang] [clang] Fix `gnu::init_priority` attribute handling for reserved values (PR #121577)

[Shafik Yaghmour via cfe-commits]

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@@ -33,23 +33,22 @@ Two goo __attribute__((init_priority(2,3))) ( 5, 6 ); // expected-error {{'init_
 
 Two coo[2]  __attribute__((init_priority(100)));
 #if !defined(SYSTEM)
-  // expected-error at -2 {{'init_priority' attribute requires integer constant between 101 and 65535 inclusive}}
+  // expected-error at -2 {{requested 'init_priority' 100 is reserved for internal use}}
   // unknown-warning at -3 {{unknown attribute 'init_priority' ignored}}
 #endif
 
-Two boo[2]  __attribute__((init_priority(65536)));
-#if !defined(SYSTEM)
- // expected-error at -2 {{'init_priority' attribute requires integer constant between 101 and 65535 inclusive}}
- // unknown-warning at -3 {{unknown attribute 'init_priority' ignored}}
-#endif
+Two zoo[2]  __attribute__((init_priority(-1))); // expected-error {{'init_priority' attribute requires integer constant between 0 and 65535 inclusive}}
+// unknown-warning at -1 {{unknown attribute 'init_priority' ignored}}
+
+Two boo[2]  __attribute__((init_priority(65536))); // expected-error {{'init_priority' attribute requires integer constant between 0 and 65535 inclusive}}
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shafik wrote:

Can we also test `65535` which should be valid, just for completeness sake.

https://github.com/llvm/llvm-project/pull/121577