perf tools build broken for RISCV 32 bit

[Emiliano Ingrassia]

Hi,

When building perf for RISCV 32 bit (v5.10.7) I got the following

| In file included from bench/futex-hash.c:29:
| bench/futex.h: In function ‘futex_wait’:
| bench/futex.h:37:10: error: ‘SYS_futex’ undeclared (first use in this function); did you mean ‘SYS_tee’?

This issue is similar to the one reported in https://lkml.org/lkml/2019/4/19/631

I found that patching tools/arch/riscv/include/uapi/asm/unistd.h as following:

 #ifdef __LP64__
 #define __ARCH_WANT_NEW_STAT
 #define __ARCH_WANT_SET_GET_RLIMIT
+#else
+#define __ARCH_WANT_TIME32_SYSCALLS
 #endif /* __LP64__ */

solved the problem.

I also found that a similar patch for arch/riscv/include/uapi/asm/unistd.h
was removed in commit d4c08b9776b3, so probably this is not the right way(?).

Thank you, best regards.