SystemTools: add a clonefile optimization on macOS

Implement the copy file optimization on Darwin for copy_file and copy_file_if_different. Use the copyfile API on macOS 10.5 or newer to copy the file using APFS clone semantics. This is a best effort operation, but will fallback to copying without the cloning if necessary. The operation has been available since 10.5, making it old enough to assume present as the OS has been EOLed for years now.

Ported from cmake/cmake!7325 (closed).

Author: @compnerd

assigned to @brad.king

mentioned in merge request cmake/cmake!7325 (closed)

This causes a test failure in CMake, as discussed in cmake/cmake!7325 (comment 1197452). I'll close this MR while we work this out in CMake before bringing the change upstream here.

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• ce02ac1e - SystemTools: add a clonefile optimization on macOS

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• 0969597d - SystemTools: add a clonefile optimization on macOS

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merged

mentioned in commit 9b65e88d

mentioned in merge request cmake/cmake!7345 (merged)

mentioned in issue cmake/cmake#24577 (closed)

mentioned in merge request !281 (merged)

mentioned in merge request !303 (merged)