From `zig build-exe --help`:
-fno-builtin Disable implicit builtin knowledge of functions
It seems entirely reasonable and even expected that this option should imply
both no-builtins on functions (which disables transformation of recognized code
patterns to libcalls) and nobuiltin on call sites (which disables transformation
of libcalls to intrinsics). We now match Clang's behavior for -fno-builtin.
In both cases, we're painting with a fairly broad brush by applying this to an
entire module, but it's better than nothing. #21833 proposes a more fine-grained
way to apply nobuiltin.
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