[OpenMP] kmp_affinity.h: add RISCV64 support

In D135552 the #else is added, which causes build error when
building openmp on RISCV64. This patch fixed the error:
   "Unknown or unsupported architecture"

Reviewed By: pirama

Differential Revision: https://reviews.llvm.org/D138241

Author: yabinc

openmp/runtime/src/kmp_affinity.h

@@ -267,6 +267,17 @@ class KMPHwlocAffinity : public KMPAffinity {
 #elif __NR_sched_getaffinity != 123
 #error Wrong code for getaffinity system call.
 #endif /* __NR_sched_getaffinity */
+#elif KMP_ARCH_RISCV64
+#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_* */