[Sanitizer] Fix the implementation of internal_fstat on LoongArch

If `pathname` is an empty string and the AT_EMPTY_PATH flag is specified in `flags`,
statx `pathname` argument is of type `const char *restrict`, so it should be `""`
instead of `0`.

Reviewed By: SixWeining, xen0n, xry111, lixing-star

Differential Revision: https://reviews.llvm.org/D138414

GitOrigin-RevId: dcefbce28109716803e8c83db1bd8d1bd0b6f369
1 file changed