Erroneous usage of `-Ctarget-cpu=native` during source build process

[Max Gilmour]

Thanks to liushuyu-011 for pointing out the issue here: https://code.launchpad.net/~maxgmr/ubuntu/+source/rust-safe-arch/+git/rust-safe-arch/+merge/483266/comments/1310481

In all release versions of this crate, the `-Ctarget-cpu=native` flag is used during compilation of the library crate. As liushuyu-011 details in the above linked comment, this is a bad idea because the program will crash on systems without the CPU features possessed by the Launchpad build system.

0.7.2-2 Buildlog: https://launchpadlibrarian.net/739168838/buildlog_ubuntu-oracular-amd64.rust-safe-arch_0.7.2-2_BUILDING.txt.gz
0.7.1-3 Buildlog: https://launchpadlibrarian.net/694434984/buildlog_ubuntu-noble-amd64.rust-safe-arch_0.7.1-3_BUILDING.txt.gz