wire up vdso clock_gettime for riscv32 and riscv64

arch/riscv32/syscall_arch.h

@@ -73,8 +73,7 @@ static inline long __syscall6(long n, long a, long b, long c, long d, long e, lo
 }
 
 #define VDSO_USEFUL
-/* We don't have a clock_gettime function.
 #define VDSO_CGT_SYM "__vdso_clock_gettime"
-#define VDSO_CGT_VER "LINUX_2.6" */
+#define VDSO_CGT_VER "LINUX_4.15"
 
 #define IPC_64 0

arch/riscv64/syscall_arch.h

@@ -71,8 +71,7 @@ static inline long __syscall6(long n, long a, long b, long c, long d, long e, lo
 }
 
 #define VDSO_USEFUL
-/* We don't have a clock_gettime function.
 #define VDSO_CGT_SYM "__vdso_clock_gettime"
-#define VDSO_CGT_VER "LINUX_2.6" */
+#define VDSO_CGT_VER "LINUX_4.15"
 
 #define IPC_64 0