Initial libsanitizer support for LoongArch. It survived all GCC UBSan tests.
Major changes:
- LoongArch port of Linux kernel only supports statx for stat and its families. So we need to add statx_to_stat and use it for stat-like libcalls. The logic is "borrowed" from Glibc.
- sanitizer_syscall_linux_loongarch64.inc is mostly duplicated from RISC-V port, as the syscall interface is almost same.
Nit: tab -> spaces