libroot: Use getentropy to initialize the stack protector.

Now that it's in libroot, we don't need to invoke the syscall directly.

src/system/libroot/os/stack_protector.cpp

@@ -8,9 +8,7 @@
 #include <signal.h>
 #include <stdlib.h>
 #include <sys/cdefs.h>
-#include <syscalls.h>
 
-#include "private/system/random_defs.h"
 #include "private/system/symbol_visibility.h"
 
 
@@ -25,14 +23,8 @@ __init_stack_protector()
 	if (__stack_chk_guard != 0)
 		return;
 
-	struct random_get_entropy_args args;
-	args.buffer = &__stack_chk_guard;
-	args.length = sizeof(__stack_chk_guard);
-
-	status_t status = _kern_generic_syscall(RANDOM_SYSCALLS, RANDOM_GET_ENTROPY,
-		&args, sizeof(args));
-
-	if (status != B_OK || args.length != sizeof(__stack_chk_guard)) {
+	int status = getentropy(&__stack_chk_guard, sizeof(__stack_chk_guard));
+	if (status != 0) {
 		unsigned char* p = (unsigned char *)&__stack_chk_guard;
 		p[0] = 0;
 		p[1] = 0;