cmake: avoid `-Wnonnull` warning in `HAVE_FSETXATTR_5` detection

Seen in Android 21/35 CI jobs:
```
curl/CMake/CurlTests.c:315:16: warning: null passed to a callee that requires a non-null argument [-Wnonnull]
   315 |   fsetxattr(0, 0, 0, 0, 0);
       |                ^
 1 warning generated.
```
Ref: https://github.com/curl/curl/actions/runs/13460225795/job/37613494183#step:9:5978

Follow-up to bd9f9b085aa242a5e93be0b2da96ce498d7813c4 #16377
Closes #16427

diff --git a/CMake/CurlTests.c b/CMake/CurlTests.c
index b11d0c6dd1b38e2373f6f79a316b8b90d0a1a17e..69a996a0477d4ec314e7f01c2617d49625ca3af9 100644 (file)
--- a/CMake/CurlTests.c
+++ b/CMake/CurlTests.c
@@ -312,7 +312,7 @@ int main(void)
 #include <sys/xattr.h> /* header from libc, not from libattr */
 int main(void)
 {
-  fsetxattr(0, 0, 0, 0, 0);
+  fsetxattr(0, "", 0, 0, 0);
   return 0;
 }
 #endif