[NaCl SDK] Enable linux host build for nacl_io and nacl_io_tests.

native_client_sdk/src/libraries/nacl_io/kernel_wrap_glibc.cc

Index: native_client_sdk/src/libraries/nacl_io/kernel_wrap_glibc.cc
diff --git a/native_client_sdk/src/libraries/nacl_io/kernel_wrap_glibc.cc b/native_client_sdk/src/libraries/nacl_io/kernel_wrap_glibc.cc
index 8c270b1da6ba7af9cc5862ff2d698f613f0acb5a..fc3eb544a7c27b5d63a4cd728c16fd1566ffa51c 100644
--- a/native_client_sdk/src/libraries/nacl_io/kernel_wrap_glibc.cc
+++ b/native_client_sdk/src/libraries/nacl_io/kernel_wrap_glibc.cc
@@ -388,12 +388,6 @@ int _real_write(int fd, const void *buf, size_t count, size_t *nwrote) {
   return REAL(write)(fd, buf, count, nwrote);
 }
 
-uint64_t usec_since_epoch() {
-  struct timeval tv;
-  gettimeofday(&tv, NULL);
-  return tv.tv_usec + (tv.tv_sec * 1000000);
-}
-
 static bool s_wrapped = false;
 void kernel_wrap_init() {
   if (!s_wrapped) {