LibC: Add dummy functions for rename() and strftime()

I don't really want to implement them right now, but they are required
to exist for some ports.

libc/stdio.cpp

@@ -1,3 +1,6 @@
+#include <BAN/Assert.h>
+#include <BAN/Debug.h>
+
 #include <bits/printf.h>
 #include <errno.h>
 #include <fcntl.h>
@@ -603,7 +606,11 @@ int remove(const char* path)
 }
 
 // TODO
-int rename(const char*, const char*);
+int rename(const char* old, const char* _new)
+{
+    dwarnln("rename({}, {})", old, _new);
+    ASSERT_NOT_REACHED();
+}
 
 void rewind(FILE* file)
 {

libc/time.cpp

@@ -1,3 +1,6 @@
+#include <BAN/Assert.h>
+#include <BAN/Debug.h>
+
 #include <sys/syscall.h>
 #include <time.h>
 #include <unistd.h>
@@ -75,3 +78,9 @@ struct tm* localtime(const time_t* timer)
 	// FIXME: support timezones
 	return gmtime(timer);
 }
+
+size_t strftime(char* __restrict s, size_t maxsize, const char* __restrict format, const struct tm* __restrict timeptr)
+{
+    dwarnln("strftime({}, {}, {}, {})", s, maxsize, format, timeptr);
+    ASSERT_NOT_REACHED();
+}