Add emscripten_wasm_eh cfg flag and use it to adjust the libraries

Author: hoodmane

compiler/rustc_session/src/config/cfg.rs

@@ -143,6 +143,7 @@ pub(crate) fn disallow_cfgs(sess: &Session, user_cfgs: &Cfg) {
             | (sym::target_has_atomic_load_store, Some(_))
             | (sym::target_thread_local, None) => disallow(cfg, "--target"),
             (sym::fmt_debug, None | Some(_)) => disallow(cfg, "-Z fmt-debug"),
+            (sym::emscripten_wasm_eh, None | Some(_)) => disallow(cfg, "-Z emscripten_wasm_eh"),
             _ => {}
         }
     }
@@ -295,6 +296,9 @@ pub(crate) fn default_configuration(sess: &Session) -> Cfg {
         ins_none!(sym::ub_checks);
     }
 
+    if sess.opts.unstable_opts.emscripten_wasm_eh {
+        ins_none!(sym::emscripten_wasm_eh);
+    }
     ret
 }
 

compiler/rustc_span/src/symbol.rs

@@ -823,6 +823,7 @@ symbols! {
         emit_enum_variant_arg,
         emit_struct,
         emit_struct_field,
+        emscripten_wasm_eh,
         enable,
         encode,
         end,

library/panic_unwind/src/lib.rs

@@ -31,7 +31,10 @@ use core::any::Any;
 use core::panic::PanicPayload;
 
 cfg_if::cfg_if! {
-    if #[cfg(target_os = "hermit")] {
+    if #[cfg(all(target_os = "emscripten", not(emscripten_wasm_eh)))] {
+        #[path = "emcc.rs"]
+        mod imp;
+    } else if #[cfg(target_os = "hermit")] {
         #[path = "hermit.rs"]
         mod imp;
     } else if #[cfg(target_os = "l4re")] {

library/unwind/src/lib.rs

@@ -3,7 +3,10 @@
 #![feature(link_cfg)]
 #![feature(staged_api)]
 #![cfg_attr(not(target_env = "msvc"), feature(libc))]
-#![cfg_attr(all(target_family = "wasm"), feature(simd_wasm64, wasm_exception_handling_intrinsics))]
+#![cfg_attr(
+    all(target_family = "wasm", any(not(target_os = "emscripten"), emscripten_wasm_eh)),
+    feature(simd_wasm64, wasm_exception_handling_intrinsics)
+)]
 #![allow(internal_features)]
 
 // Force libc to be included even if unused. This is required by many platforms.