[clang] [clang][analyzer] Improve 'errno' modeling of 'mkdtemp' (PR #76671)

[Balázs Kéri via cfe-commits]

================
@@ -54,3 +51,25 @@ int errno_lseek(int fildes, off_t offset) {
   }
   return 0;
 }
+
+void errno_mkstemp(char *template) {
+  int FD = mkstemp(template);
+  if (FD >= 0) {
+    if (errno) {}                    // expected-warning{{An undefined value may be read from 'errno'}}
+    close(FD);
+  } else {
+    clang_analyzer_eval(FD == -1);   // expected-warning{{TRUE}}
+    clang_analyzer_eval(errno != 0); // expected-warning{{TRUE}}
+    if (errno) {}                    // no warning
+  }
+}
+
+void errno_mkdtemp(char *template) {
+  char *Dir = mkdtemp(template);
+  if (Dir == NULL) {
+    clang_analyzer_eval(errno != 0); // expected-warning{{TRUE}}
+    if (errno) {}                    // no warning
+  } else {
----------------
balazske wrote:

```suggestion
  } else {
    `clang_analyzer_eval(Dir == template); // expected-warning{{TRUE}}`
```

https://github.com/llvm/llvm-project/pull/76671