[clang] [clang] Warn on umask() argument bits outside 0777 (PR #198130)

[Aaron Ballman via cfe-commits]

================
@@ -3800,6 +3800,14 @@ def VFork : LibBuiltin<"unistd.h"> {
   let Prototype = "pid_t()";
 }
 
+// POSIX sys/stat.h
+
+def Umask : LibBuiltin<"sys/stat.h"> {
+  let Spellings = ["umask"];
+  let Attributes = [IgnoreSignature];
+  let Prototype = "";
----------------
AaronBallman wrote:

```suggestion
  let Prototype = "mode_t(mode_t)";
```
Just so folks have an idea what the signature is even though we ignore it.

https://github.com/llvm/llvm-project/pull/198130