add setresuid/setresgid functions (nonstandard)

include/unistd.h

@@ -154,6 +154,8 @@ int sethostname(const char *, size_t);
 int usleep(unsigned);
 unsigned ualarm(unsigned, unsigned);
 int setgroups(int, const gid_t []);
+int setresuid(uid_t, uid_t, uid_t);
+int setresgid(gid_t, gid_t, gid_t);
 #endif
 
 #define _XOPEN_VERSION          700

src/unistd/setresgid.c

+#define _GNU_SOURCE
+#include <unistd.h>
+#include "syscall.h"
+#include "libc.h"
+
+int setresgid(gid_t rgid, gid_t egid, gid_t sgid)
+{
+	if (libc.rsyscall) return libc.rsyscall(__NR_setresgid, rgid, egid, sgid, 0, 0, 0);
+	return syscall(SYS_setresgid, rgid, egid, sgid);
+}

src/unistd/setresuid.c

+#define _GNU_SOURCE
+#include <unistd.h>
+#include "syscall.h"
+#include "libc.h"
+
+int setresuid(uid_t ruid, uid_t euid, uid_t suid)
+{
+	if (libc.rsyscall) return libc.rsyscall(__NR_setresuid, ruid, euid, suid, 0, 0, 0);
+	return syscall(SYS_setresuid, ruid, euid, suid);
+}