[libc] Add new libc

This new libc is mostly from scratch, with *printf() functions provided
by Marco Paland and Eyal Rozenberg's tiny printf library, and malloc and
friends provided by dlmalloc.

src/libraries/libc/__j6libc/bits.h

@@ -0,0 +1,41 @@
+#pragma once
+/** \file j6libc/bits.h
+  * Internal helpers for bitwise math.
+  *
+  * This file is part of the C standard library for the jsix operating
+  * system.
+  *
+  * This Source Code Form is subject to the terms of the Mozilla Public
+  * License, v. 2.0. If a copy of the MPL was not distributed with this
+  * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+  */
+
+#ifndef __cplusplus
+#error "__j6libc/bits.h included by non-C++ code"
+#endif
+
+#include <stdint.h>
+#include <__j6libc/size_t.h>
+
+namespace __j6libc {
+
+constexpr size_t log2(size_t n) {
+    return n < 2 ? 1 : 1 + log2(n/2);
+}
+
+constexpr size_t word_bytes = sizeof(void*);
+constexpr size_t word_bits  = word_bytes << 3;
+constexpr uintptr_t word_align_mask  = word_bytes - 1;
+constexpr unsigned word_shift = log2(word_bytes);
+
+template <typename T>
+inline bool is_aligned(uintptr_t addr) {
+    return (addr & (sizeof(T)-1)) == 0;
+}
+
+template <typename T, typename S>
+inline bool is_aligned(S *p) {
+    return is_aligned<T>(reinterpret_cast<uintptr_t>(p));
+}
+
+} // namespace __j6libc