arch/sim: replace macOS C++ constructor runtime hack with post-link patch

The sim architecture needs to defer C++ global constructors until after
NuttX kernel initialization completes. On macOS this was previously done
via a runtime hack (sim_macho_init.c): a __attribute__((constructor))
function intercepted constructors, saved them, and replayed them later.
That approach was fragile because it depended on constructor ordering
and required mprotect() to patch the read-only __mod_init_func section
at runtime.

This commit replaces the runtime hack with a post-link patching scheme:

  1. Link with -Wl,-ld_classic,-no_fixup_chains to keep the classic
     __mod_init_func pointer format (prevents ld64 from converting it
     to __init_offsets).
  2. Post-link, run patch_macho_initsection.py (python3 + lief) to
     patch Mach-O section type flags from
     MOD_INIT_FUNC_POINTERS/INIT_FUNC_OFFSETS to REGULAR, so dyld
     skips them entirely.
  3. Use the Mach-O auto-generated boundary symbols
     section$start$__DATA_CONST$__mod_init_func /
     section$end$__DATA_CONST$__mod_init_func, mapped via __asm()
     labels in arch/sim/include/arch.h to the common _sinit[]/_einit[]
     names used by lib_cxx_initialize().

Linux behavior is unchanged.

Changes:
  - arch/sim/include/arch.h: add macOS __asm() declarations for
    _sinit/_einit
  - arch/sim/src/Makefile: drop sim_macho_init.c HEADSRC handling,
    always pass -ld_classic,-no_fixup_chains on macOS, run
    patch_macho_initsection.py after link when CONFIG_HAVE_CXXINITIALIZE
  - arch/sim/src/sim/CMakeLists.txt: same for the CMake build
  - arch/sim/src/patch_macho_initsection.py: new lief-based patcher
  - arch/sim/src/sim/posix/sim_macho_init.c: deleted (135-line hack)
  - libs/libc/misc/lib_cxx_initialize.c: remove
    macho_call_saved_init_funcs special case; single unified loop

Testing:
  - macOS (Ventura VM): verified lief patching with standalone test
    (test_sinit7) confirming the constructor is deferred past main()
    and only invoked when explicitly called via the _sinit/_einit loop.

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>

arch/sim/src/patch_macho_initsection.py

@@ -0,0 +1,72 @@
+#!/usr/bin/env python3
+############################################################################
+# arch/sim/src/patch_macho_initsection.py
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.  The
+# ASF licenses this file to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance with the
+# License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+# implied.  See the License for the specific language governing
+# permissions and limitations under the License.
+#
+############################################################################
+
+"""Patch Mach-O init section type flags to prevent dyld from
+auto-running C++ constructors.
+
+Changes MOD_INIT_FUNC_POINTERS (0x9) section types to REGULAR (0x0)
+so that dyld ignores them.  NuttX will invoke the constructors
+explicitly from lib_cxx_initialize().
+
+Requires: pip install lief
+"""
+
+import argparse
+import sys
+
+try:
+    import lief
+except ImportError:
+    print(
+        "Error: lief is required. Install with: pip install lief",
+        file=sys.stderr,
+    )
+    sys.exit(1)
+
+
+def main():
+    parser = argparse.ArgumentParser(description="Patch Mach-O init section type flags")
+    parser.add_argument("binary", help="Path to the Mach-O binary")
+    args = parser.parse_args()
+
+    binary = lief.MachO.parse(args.binary)
+    if binary is None:
+        print(f"Error: failed to parse {args.binary}", file=sys.stderr)
+        sys.exit(1)
+
+    fat = binary.at(0)
+    T = lief.MachO.Section.TYPE
+    patched = 0
+    for section in fat.sections:
+        if section.type == T.MOD_INIT_FUNC_POINTERS:
+            section.type = T.REGULAR
+            patched += 1
+
+    if patched:
+        fat.write(args.binary)
+
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())