[fuchsia] Update zx_time_get syscalls.

[cryptoad]

Summary

Fuchsia renamed its zx_time_get syscall to zx_clock_get, so we update
the calls here.

[cryptoad]

Unless I am missing something, I think it's already in with https://reviews.llvm.org/D42617 (https://github.com/llvm-mirror/compiler-rt/blob/master/lib/sanitizer_common/sanitizer_fuchsia.cc#L52)

lib/sanitizer_common/sanitizer_fuchsia.cc

static void internal_nanosleep(zx_time_t ns) {
   CHECK_EQ(status, ZX_OK);
 }
 
 unsigned int internal_sleep(unsigned int seconds) {
   internal_nanosleep(ZX_SEC(seconds));
   return 0;
 }
 
-u64 NanoTime() { return _zx_time_get(ZX_CLOCK_UTC); }
+u64 NanoTime() { return zx_clock_get(ZX_CLOCK_UTC); }
 
-u64 MonotonicNanoTime() { return _zx_time_get(ZX_CLOCK_MONOTONIC); }
+u64 MonotonicNanoTime() { return zx_clock_get(ZX_CLOCK_MONOTONIC); }
 
 uptr internal_getpid() {
   zx_info_handle_basic_t info;
   zx_status_t status =
       _zx_object_get_info(_zx_process_self(), ZX_INFO_HANDLE_BASIC, &info,
                           sizeof(info), NULL, NULL);
   CHECK_EQ(status, ZX_OK);
   uptr pid = static_cast<uptr>(info.koid);