override the have_lse boolean in compiler_rt in start.zig after checking the auxval for what CPU features are available

[andrewrk]

On aarch64-linux, this boolean flag should be set to true in start code after checking the aux val and determining that the CPU features include lse.

zig/lib/compiler_rt/aarch64_outline_atomics.zig

Lines 7 to 11 in 670b4c5

	/// This default is overridden at runtime after inspecting CPU properties.
	/// It is intentionally not exported in order to make the machine code that
	/// uses it a statically predicted direct branch rather than using the PLT,
	/// which ARM is concerned would have too much overhead.
	var __aarch64_have_lse_atomics: u8 = @boolToInt(always_has_lse);

Instead of using a constructor like libgcc, zig will export a function for setting this flag explicitly.