Remove --fatal-warnings on wasm targets

These were added with good intentions, but a recent change in LLVM 18 emits a warning while examining .rmeta sections in .rlib files. Since this flag is a nice-to-have and users can update their LLVM linker independently of rustc's LLVM version, we can just omit the flag.

Author: djkoloski

compiler/rustc_target/src/spec/base/wasm.rs

@@ -38,9 +38,6 @@ pub fn options() -> TargetOptions {
  // supposed to be imported and have all other symbols generate errors if
  // they remain undefined.
  concat!($prefix, "--allow-undefined"),
- // Rust code should never have warnings, and warnings are often
- // indicative of bugs, let's prevent them.
- concat!($prefix, "--fatal-warnings"),
  // LLD only implements C++-like demangling, which doesn't match our own
  // mangling scheme. Tell LLD to not demangle anything and leave it up to
  // us to demangle these symbols later. Currently rustc does not perform

compiler/rustc_target/src/spec/targets/wasm32_unknown_emscripten.rs

@@ -5,10 +5,7 @@ use crate::spec::{
 pub fn target() -> Target {
  // Reset flags for non-Em flavors back to empty to satisfy sanity checking tests.
  let pre_link_args = LinkArgs::new();
- let post_link_args = TargetOptions::link_args(
- LinkerFlavor::EmCc,
- &["-sABORTING_MALLOC=0", "-Wl,--fatal-warnings"],
- );
+ let post_link_args = TargetOptions::link_args(LinkerFlavor::EmCc, &["-sABORTING_MALLOC=0"]);
 
  let opts = TargetOptions {
  os: "emscripten".into(),