Function spirv_std::memcmp

#[no_mangle]pub unsafe extern "C" fn memcmp(s1: *const u8, s2: *const u8, n: usize) -> i32

libcore requires a few external symbols to be defined: https://github.com/rust-lang/rust/blob/c2bc344eb23d8c1d18e803b3f1e631cf99926fbb/library/core/src/lib.rs#L23-L27 TODO: This is copied from compiler_builtins/mem.rs. Can we use that one instead? The note in the above link says “[the symbols] can also be provided by the compiler-builtins crate”. The memcpy in compiler_builtins is behind a “mem” feature flag - can we enable that somehow? https://github.com/rust-lang/compiler-builtins/blob/eff506cd49b637f1ab5931625a33cef7e91fbbf6/src/mem.rs#L12-L13