[libc] NFC: Fix build on systems that don't have linux/time_types.h

This broke some bots that don't have linux/time_types.h available
(libc-x86_64-debian-*).

The header is needed because of __kernel_timespec, and since this is
only needed when SYS_sched_rr_get_interval_time64 is available, guarding
the include should fix the broken bot.

Author: mikhailramalho

libc/src/sched/linux/sched_rr_get_interval.cpp

@@ -12,9 +12,12 @@
 #include "src/__support/common.h"
 #include "src/errno/libc_errno.h"
 
-#include <linux/time_types.h> // For __kernel_timespec.
 #include <sys/syscall.h> // For syscall numbers.
 
+#ifdef SYS_sched_rr_get_interval_time64
+#include <linux/time_types.h> // For __kernel_timespec.
+#endif
+
 namespace __llvm_libc {
 
 LLVM_LIBC_FUNCTION(int, sched_rr_get_interval,