Fix macOS arm64 (Apple Silicon) linker support

[metaneutrons]

Summary

Fix linking on macOS arm64 (Apple Silicon, M1/M2/M3/M4).

Changes (3 files, +47/-11)

makefile:

• Normalize arm64 (from uname -m) to aarch64 before the 32-bit armv% catch-all

src/compiler/fbc.bas:

• line input in hGet1stOutputLineFromCommand (handles spaces in SDK paths)
• Add -arch arm64 for FB_CPUFAMILY_AARCH64 on darwin
• Replace deprecated -macosx_version_min with -platform_version macos <min> <sdk>
  • min: 11.0 for arm64, 10.4 for x86_64 (preserves original minimum)
  • sdk: detected via xcrun --show-sdk-version (fallback 14.0)
• SDK path via xcrun --show-sdk-path (only on darwin host, respects user -sysroot, quoted with QUOTE)
• Skip GNU --sysroot= on darwin (Apple ld uses -syslibroot)
• Remove --eh-frame-hdr on darwin (unsupported by Apple ld)
• Remove -lgcc from darwin default libs (unavailable with Apple clang)

src/rtlib/profile_cycles.c:

• Guard ELF __start_/__stop_ section boundary symbol declarations and usage with !defined(HOST_DARWIN)
• Provide data=NULL, length=0 fallback on darwin (cycle profiling compiles but produces no output)

Testing

make bootstrap-minimal ENABLE_STANDALONE=1

Successfully builds fbc and runtime library on macOS 15 (Sequoia) with Apple clang 21 on M4.

Notes

• x86_64 darwin builds unaffected (minimum version preserved at 10.4)
• -profile cycles compiles on darwin but produces no per-procedure data (Mach-O lacks ELF section boundary symbols)
• Bootstrap requires bootstrap/darwin-aarch64/ (copy from bootstrap/linux-aarch64/ + fix clang computed goto)

[Copilot]

Pull request overview

This PR updates the build/link logic to support successful linking on macOS arm64 (Apple Silicon) by adjusting architecture detection and Darwin-specific linker flags/behaviors.

Changes:

• Normalize arm64 to aarch64 in the makefile’s TARGET_ARCH detection before the 32-bit ARM normalization.
• Update the Darwin linker invocation in fbc.bas to add -arch arm64 for AArch64 and use modern -platform_version/-syslibroot behavior (including xcrun SDK detection on Darwin hosts), while avoiding GNU-ld-only flags/libs on Darwin.
• Make cycle profiling compile on Darwin by disabling ELF section-boundary-symbol usage and emitting an empty report payload.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
makefile	Normalizes arm64 → aarch64 ahead of 32-bit ARM matching to select the correct target CPU family on macOS Apple Silicon.
src/compiler/fbc.bas	Adjusts Darwin link flags for arm64 and modern Apple ld usage (SDK/sysroot handling, platform version, and default libs).
src/rtlib/profile_cycles.c	Guards ELF __start/__stop usage on Darwin and provides a safe no-data fallback so it compiles on Mach-O.

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