RISC-V: Using SYS_clock_gettime64 for rv32 libgloss.

- RISC-V 32 bits linux/glibc didn't provide gettimeofday anymore
   after upstream, because RV32 didn't have backward compatible issue,
   so RV32 only support 64 bits time related system call.

 - So using clock_gettime64 call instead for rv32 libgloss.

libgloss/riscv/machine/syscall.h

@@ -44,6 +44,7 @@
 #define SYS_munmap 215
 #define SYS_mremap 216
 #define SYS_mmap 222
+#define SYS_clock_gettime64 403
 #define SYS_open 1024
 #define SYS_link 1025
 #define SYS_unlink 1026

libgloss/riscv/sys_gettimeofday.c

@@ -1,10 +1,31 @@
 #include <machine/syscall.h>
 #include <sys/time.h>
+#include <stdint.h>
 #include "internal_syscall.h"
 
 /* Get the current time.  Only relatively correct.  */
 int
 _gettimeofday(struct timeval *tp, void *tzp)
 {
+#if __riscv_xlen == 32
+  struct __timespec64
+  {
+    int64_t tv_sec;         /* Seconds */
+# if BYTE_ORDER == BIG_ENDIAN
+    int32_t __padding;      /* Padding */
+    int32_t tv_nsec;        /* Nanoseconds */
+# else
+    int32_t tv_nsec;        /* Nanoseconds */
+    int32_t __padding;      /* Padding */
+# endif
+  };
+  struct __timespec64 ts64;
+  int rv;
+  rv = syscall_errno (SYS_clock_gettime64, 2, 0, (long)&ts64, 0, 0, 0, 0);
+  tp->tv_sec = ts64.tv_sec;
+  tp->tv_usec = ts64.tv_nsec * 1000;
+  return rv;
+#else
   return syscall_errno (SYS_gettimeofday, 1, tp, 0, 0, 0, 0, 0);
+#endif
 }