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, 5 insertions, 1 deletions

diff --git a/kernel/lib/cxxabi.cpp b/kernel/lib/cxxabi.cpp
index 8a96628..6d422e3 100644
--- a/kernel/lib/cxxabi.cpp
+++ b/kernel/lib/cxxabi.cpp
@@ -74,6 +74,10 @@ void  operator delete[](void* ptr) noexcept { (void)ptr; /* TODO: kfree */ }
 void  operator delete(void* ptr, size_t)   noexcept { (void)ptr; /* TODO: kfree */ }
 void  operator delete[](void* ptr, size_t) noexcept { (void)ptr; /* TODO: kfree */ }
 
-/* Placement new — doesn't allocate, just returns the pointer */
+/* Placement new — doesn't allocate, just returns the pointer.
+ * Guarded to avoid conflict with <new> header's placement new. */
+#ifndef _LIBBASTION_PLACEMENT_NEW_DEFINED
+#define _LIBBASTION_PLACEMENT_NEW_DEFINED
 inline void* operator new(size_t, void* ptr)    noexcept { return ptr; }
 inline void* operator new[](size_t, void* ptr)  noexcept { return ptr; }
+#endif