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, 18 insertions, 0 deletions

diff --git a/kernel/lib/string.cpp b/kernel/lib/string.cpp
index 3bd60fa..1365147 100644
--- a/kernel/lib/string.cpp
+++ b/kernel/lib/string.cpp
@@ -75,4 +75,22 @@ char* strncpy(char* dest, const char* src, size_t n) {
     return dest;
 }
 
+void* memchr(const void* s, int c, size_t n) {
+    auto* p = static_cast<const uint8_t*>(s);
+    auto uc = static_cast<uint8_t>(c);
+    for (size_t i = 0; i < n; i++)
+        if (p[i] == uc) return const_cast<void*>(static_cast<const void*>(p + i));
+    return nullptr;
+}
+
+int strncmp(const char* s1, const char* s2, size_t n) {
+    const auto* u1 = reinterpret_cast<const uint8_t*>(s1);
+    const auto* u2 = reinterpret_cast<const uint8_t*>(s2);
+    for (size_t i = 0; i < n; i++) {
+        if (u1[i] != u2[i]) return static_cast<int>(u1[i]) - static_cast<int>(u2[i]);
+        if (u1[i] == 0) break;
+    }
+    return 0;
+}
+
 } // extern "C"