Rollup merge of #105468 - sunfishcode:sunfishcode/main-void-wasi, r=estebank

Mangle "main" as "__main_void" on wasm32-wasi

On wasm, the age-old C trick of having a main function which can either have no arguments or argc+argv doesn't work, because wasm requires caller and callee signatures to match. WASI's current strategy is to have compilers mangle main's name to indicate which signature they're using. Rust uses the no-argument form, which should be mangled as `__main_void`.

This is needed on wasm32-wasi as of #105395.

compiler/rustc_target/src/spec/wasm32_wasi.rs

@@ -104,6 +104,10 @@ pub fn target() -> Target {
     // `args::args()` makes the WASI API calls itself.
     options.main_needs_argc_argv = false;
 
+    // And, WASI mangles the name of "main" to distinguish between different
+    // signatures.
+    options.entry_name = "__main_void".into();
+
     Target {
         llvm_target: "wasm32-wasi".into(),
         pointer_width: 32,