Is there way to disable LTO?

[maiden mason]

in what context?

[balmy spire]

what is LTO ?

[glass pollen]

Link Time Optimization.
It undoes one of ramifications of compiling your code into multiple compiliation units and linking them together at the end.
That mainly being the fact that function calls aren't generally inlined across compilation units.

AFAIK though, Zig compiles all Zig code as one unit, and so it's not necessary for purely Zig code.

If you're compiling C and Zig though, then you would want it if you want inlining between the two.