y2038: Introduce struct __timeval64 - new internal glibc type

This type is a glibc's "internal" type similar to struct timeval but
whose tv_sec field is a __time64_t rather than a time_t, which makes it
Y2038-proof. This struct is NOT supposed to be passed to the kernel -
instead it shall be converted to struct __timespec64 and clock_[sg]ettime
syscalls shall be used (which are now Y2038 safe).

Build tests:
./src/scripts/build-many-glibcs.py glibcs

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>

include/time.h

@@ -93,6 +93,20 @@ struct __itimerspec64
 };
 #endif
 
+#if __TIMESIZE == 64
+# define __timeval64 timeval
+#else
+/* The glibc Y2038-proof struct __timeval64 structure for a time value.
+   This structure is NOT supposed to be passed to the Linux kernel.
+   Instead, it shall be converted to struct __timespec64 and time shall
+   be [sg]et via clock_[sg]ettime (which are now Y2038 safe).  */
+struct __timeval64
+{
+  __time64_t tv_sec;         /* Seconds */
+  __suseconds64_t tv_usec;       /* Microseconds */
+};
+#endif
+
 #if __TIMESIZE == 64
 # define __ctime64 ctime
 #else