[SPM] Unsafe build flags make importing the package by version string impossible

[Kolos65]

SPM forbids depending on packages by version string if they have unsafe build flags.

The only way to use a package with unsafe flags is by specifying the exact commit hash.

Im curious if the package truly needs those flags or if they can be removed / replaced with something else.

Current unsafe flags are:

• -Wno-shorten-64-to-32: This is only to suppress warnings so its not a necessity
• -O3: Does opting for O3 optimization level make that much of a difference?
• -DNDEBUG: We can replace this with: cSettings: [.define("NDEBUG")
• -fno-objc-arc: Do we really need this? What exactly requires this flag in the project? Can it be refactored to cope with objc arc?