Fix "Too many personality routines for compact unwind" link error for iOS

[ruccho]

Background

The previous PR #152 localized the bundled mimalloc in the iOS libunienc_c.a via ld -r -exported_symbols_list _unienc* — i.e. it kept only _unienc* global and made everything else local, including the Rust runtime's exception-handling personality routines.

That over-localizes. When a downstream Xcode project statically links this .a alongside other static libraries, each lib ends up carrying its own local personality routine. The Mach-O compact-unwind format can encode at most 3 personality routines per image, so the extra copies overflow that limit and the link fails:

ld: Too many personality routines for compact unwind to encode. Found routines:

Fix

Localize only mimalloc's own symbols, and leave everything else (the _unienc* FFI entry points and the Rust runtime / personality symbols) global so the linker can coalesce them normally.

• Switched ld -r from -exported_symbols_list to -unexported_symbols_list, listing just the mimalloc symbol families:

  _mi_*
  __mi_*
  ___mi_*
  _heap_main
  _theap_main
  

  These five globs cover all 432 mimalloc symbols in the current unity-fork build with zero false positives (verified with nm).
• Renamed apple-exports.txt → apple-mimalloc-unexports.txt.

Result after localization (verified on macos-15 / ld-prime):

• mimalloc: 432 → 0 external (all local; no longer coalesces with Unity's mimalloc)
• _unienc*: 34 kept global
• Rust runtime / personality: kept global → coalesced by the linker, so no compact-unwind overflow