rune/libenclave: Work around nanosleep() issue

nanosleep() may return the remaining duration longer than
requested one due to timer slack.
Signed-off-by: Jia Zhang <zhang.jia@linux.alibaba.com>

rune/libenclave/internal/runtime/pal/pal_linux.go

 package enclave_runtime_pal // import "github.com/opencontainers/runc/libenclave/internal/runtime/pal"
 
+/*
+#include <sys/prctl.h>
+
+static void workaround_nanosleep(void) {
+	// nanosleep() may return the remaining duration longer than
+	// requested one due to timer slack.
+	prctl(PR_SET_TIMERSLACK, 1, 0, 0, 0);
+}
+*/
 import "C"
 
 import (
@@ -26,6 +35,8 @@ func (pal *enclaveRuntimePal) Init(args string, logLevel string) error {
         }
         pal.version = ver
 
+	C.workaround_nanosleep();
+
 	return api.init(args, logLevel)
 }