bastion: add freestanding C++ standard library (libcxx)feature/freestanding-libcxx

Header-only implementation of a C++ standard library subset for the
freestanding kernel, using Clang builtins wherever possible. Provides
19 public headers (~35 internal files): type_traits, utility, memory,
algorithm, functional, concepts, array, string_view, span, optional,
expected, variant, tuple, bit, limits, new, initializer_list, cstdint,
cstddef, and source_location.

Integration changes:
- kernel/Makefile: add -Ilib/libcxx/include to include path
- kernel/lib/string.cpp: add memchr and strncmp (needed by string_view)
- kernel/lib/cxxabi.cpp: guard placement new against <new> header conflict
- kernel/include/kernel/kernel.h: Panic() now uses std::source_location
- kernel/core/kernel.cpp: Panic() implementation updated to match

Builds cleanly on both x86_64 and aarch64 with zero new warnings.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

1 files changed, 76 insertions, 0 deletions

diff --git a/kernel/lib/libcxx/include/__algorithm/minmax.h b/kernel/lib/libcxx/include/__algorithm/minmax.h
new file mode 100644
index 0000000..b28d66c
--- /dev/null
+++ b/kernel/lib/libcxx/include/__algorithm/minmax.h
@@ -0,0 +1,76 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// Part of the BastionOS freestanding C++ standard library.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBBASTION_ALGORITHM_MINMAX_H
+#define _LIBBASTION_ALGORITHM_MINMAX_H
+
+#include <__config>
+#include <initializer_list>
+
+_LIBBASTION_BEGIN_NAMESPACE_STD
+
+// ── min ─────────────────────────────────────────────────────────────────────
+
+template<class _Tp>
+_LIBBASTION_NODISCARD constexpr const _Tp& min(const _Tp& __a, const _Tp& __b) {
+    return (__b < __a) ? __b : __a;
+}
+
+template<class _Tp, class _Compare>
+_LIBBASTION_NODISCARD constexpr const _Tp& min(const _Tp& __a, const _Tp& __b, _Compare __comp) {
+    return __comp(__b, __a) ? __b : __a;
+}
+
+template<class _Tp>
+_LIBBASTION_NODISCARD constexpr _Tp min(initializer_list<_Tp> __il) {
+    const _Tp* __first = __il.begin();
+    const _Tp* __last  = __il.end();
+    const _Tp* __result = __first;
+    for (++__first; __first != __last; ++__first)
+        if (*__first < *__result)
+            __result = __first;
+    return *__result;
+}
+
+// ── max ─────────────────────────────────────────────────────────────────────
+
+template<class _Tp>
+_LIBBASTION_NODISCARD constexpr const _Tp& max(const _Tp& __a, const _Tp& __b) {
+    return (__a < __b) ? __b : __a;
+}
+
+template<class _Tp, class _Compare>
+_LIBBASTION_NODISCARD constexpr const _Tp& max(const _Tp& __a, const _Tp& __b, _Compare __comp) {
+    return __comp(__a, __b) ? __b : __a;
+}
+
+template<class _Tp>
+_LIBBASTION_NODISCARD constexpr _Tp max(initializer_list<_Tp> __il) {
+    const _Tp* __first = __il.begin();
+    const _Tp* __last  = __il.end();
+    const _Tp* __result = __first;
+    for (++__first; __first != __last; ++__first)
+        if (*__result < *__first)
+            __result = __first;
+    return *__result;
+}
+
+// ── clamp ───────────────────────────────────────────────────────────────────
+
+template<class _Tp>
+_LIBBASTION_NODISCARD constexpr const _Tp& clamp(const _Tp& __v, const _Tp& __lo, const _Tp& __hi) {
+    return (__v < __lo) ? __lo : (__hi < __v) ? __hi : __v;
+}
+
+template<class _Tp, class _Compare>
+_LIBBASTION_NODISCARD constexpr const _Tp& clamp(const _Tp& __v, const _Tp& __lo, const _Tp& __hi, _Compare __comp) {
+    return __comp(__v, __lo) ? __lo : __comp(__hi, __v) ? __hi : __v;
+}
+
+_LIBBASTION_END_NAMESPACE_STD
+
+#endif // _LIBBASTION_ALGORITHM_MINMAX_H