[OpenMP] kmp_affinity.h: add LoongArch64 support

In D135552 the #else is added, which causes build error when
building openmp on LoongArch. This patch fixed the error:
      "Unknown or unsupported architecture"

Reviewed By: SixWeining, MaskRay

Differential Revision: https://reviews.llvm.org/D137604

openmp/runtime/src/kmp_affinity.h

@@ -256,6 +256,17 @@ public:
 #elif __NR_sched_getaffinity != 5196
 #error Wrong code for getaffinity system call.
 #endif /* __NR_sched_getaffinity */
+#elif KMP_ARCH_LOONGARCH64
+#ifndef __NR_sched_setaffinity
+#define __NR_sched_setaffinity 122
+#elif __NR_sched_setaffinity != 122
+#error Wrong code for setaffinity system call.
+#endif /* __NR_sched_setaffinity */
+#ifndef __NR_sched_getaffinity
+#define __NR_sched_getaffinity 123
+#elif __NR_sched_getaffinity != 123
+#error Wrong code for getaffinity system call.
+#endif /* __NR_sched_getaffinity */
 #else
 #error Unknown or unsupported architecture
 #endif /* KMP_ARCH_* */