macos: strip non-extern symbols at link time (CMake + mrbind)

[Grantim]

Summary

The wheel-size investigation found that on macOS our shipped Mach-O binaries carry their full local symbol table in __LINKEDIT. On mrmeshpy.so that's 86 MB out of 119 MB (72% of the file), with similar ratios on libMRMesh/libMRViewer/libMRVoxels/libMRMcp/libMRIOExtras/etc. Linux strips by default; only macOS doesn't.

This PR adds -Wl,-x (the linker analog of strip -x — drops local symbols, keeps externs that dyld binds) on the macOS link line for non-Debug configs, in two places:

1. cmake/Modules/CompilerOptions.cmake — add_link_options($<$<NOT:$<CONFIG:Debug>>:-Wl,-x>) in the existing Apple branch. Covers every CMake target (our libs, libMeshLibC2, in-tree thirdparty wrapped via add_subdirectory).
2. scripts/mrbind/generate.mk:243 — replaces $(if $(IS_MACOS),,-s) (which skipped strip on macOS because Apple's ld rejects -s) with $(if $(IS_MACOS),-Wl$(comma)-x,-s). Covers mrmeshpy.so and the other mrbind-generated Python bindings, which are linked outside the CMake tree.

This benefits every macOS distribution — wheels, the .pkg installer's MeshLib.framework, the runtimes/osx-*/native/ slice of NuGet, the zip distribution. Replaces #6057 (a wheel-only attempt where the strip placement was ineffective).

Verified savings — mac wheels (both archs)

	arm64	x86_64
baseline .whl	87.87 MB	91.25 MB
this PR .whl	77.86 MB	82.85 MB
compressed Δ	−10.01 MB (−11.4%)	−8.40 MB (−9.2%)

mrmeshpy.so (the dominant binary) before/after:

	arm64 baseline	arm64 PR	x86_64 baseline	x86_64 PR
File size	119.52 MB	34.88	124.59 MB	47.29
__TEXT	31.70	31.70	40.09	40.09
__LINKEDIT	86.08	1.44	82.80	5.49
Symbol count	528,811	2,958	394,251	23,858

__TEXT is byte-identical on both archs (sanity check: strip removed no code). Most of __LINKEDIT is mangled symbol names — DEFLATE crushes them ~10×, so the ~80 MB uncompressed save lands as ~9 MB compressed on the wheel.

Per-binary __LINKEDIT (arm64; x86_64 deltas are within ±10% of these):

Binary	before MB	after MB	Δ MB
mrmeshpy.so	86.08	1.44	−84.64
libMRViewer.dylib	3.31	0.63	−2.68
libMRMesh.dylib	3.04	0.60	−2.44
libMRVoxels.dylib	2.76	0.24	−2.53
libMRMcp.dylib	1.01	0.16	−0.85
mrviewerpy.so	0.50	0.06	−0.44
libMRIOExtras.dylib	0.37	0.10	−0.28
Others (mrcuda/mrmeshnumpy/MRPython/MRSymbolMesh)	0.42	0.16	−0.26

Equivalent verification on the .pkg from macos-build-test: every bundled dylib in MeshLib.framework is also stripped (e.g., libMRMesh.dylib __LINKEDIT 3.04 → 0.58 MB). mrmeshpy.so isn't in the .pkg (only the framework C++ libs + companion Python modules are), but the same lever benefits anyone consuming the framework or NuGet.

Test plan

CI under full-ci + test-pip-build produces all relevant artifacts:

• macos-build-test (arm64, Release) green
• macos-build-test (x64, Release) green
• macos-build-test (arm64, Debug) green (Debug skips strip — confirmed via generator expression)
• test-pip-build / macos-pip-build (arm64) green
• test-pip-build / macos-pip-build (x86) green
• all test-pip-build / macos-pip-test (arm64, ...) green (6 Python versions)
• all test-pip-build / macos-pip-test (x86, ...) green (6 Python versions)
• mrmeshpy.so __LINKEDIT shrinks ~98% on both archs
• __TEXT byte-identical on every binary
• Distributives_macos-arm .pkg framework dylibs also stripped

Risk

Low. -Wl,-x is the standard release-build linker option used by Apple's own SDK and most C++ projects shipping macOS dylibs. Doesn't affect dyld linkage, exception unwinding (CFI tables live in __TEXT's __unwind_info/__eh_frame), __cxa_* lookups (in __DATA_CONST), or pybind11 entry points (PyInit_* is extern). All 12 macos-pip-test jobs (2 archs × 6 Python versions) pass — import meshlib.mrmeshpy and friends all work after dyld linkage. Rollback is a one-line revert per file.

Follow-up

PR-B (separate) will strip third-party deps that we consume (vcpkg-installed libs on Linux+Windows via triplet linker flag, brew-installed dylibs on macOS via CI post-install strip).

🤖 Generated with Claude Code