Makefile: avoid cp-ing over existing executable files

On macOS, code-signing information for executables (including those signed automatically by the linker) is cached by the system on a per-inode basis. The cp(1) tool will truncate and overwrite an existing file if present, so we need to delete it first to avoid strange crashes. See https://developer.apple.com/documentation/security/updating_mac_software

RCrcombs committed 4 years ago