Remove -Zoom=panic

There are major questions remaining about the reentrancy that this
allows. It doesn't have any users on github outside of a single project
that uses it in a panic=abort project to show backtraces. It
can still be emulated through #[alloc_error_handler] or
set_alloc_error_hook depending on if you use the standard library or
not. And finally it makes it harder to do various improvements to the
allocator shim.

Author: bjorn3

src/allocator.rs

@@ -6,7 +6,6 @@ use rustc_ast::expand::allocator::{
     AllocatorMethod, AllocatorTy, NO_ALLOC_SHIM_IS_UNSTABLE, default_fn_name, global_fn_name,
 };
 use rustc_codegen_ssa::base::{allocator_kind_for_codegen, allocator_shim_contents};
-use rustc_session::config::OomStrategy;
 use rustc_symbol_mangling::mangle_internal_symbol;
 
 use crate::prelude::*;
@@ -15,16 +14,11 @@ use crate::prelude::*;
 pub(crate) fn codegen(tcx: TyCtxt<'_>, module: &mut dyn Module) -> bool {
     let Some(kind) = allocator_kind_for_codegen(tcx) else { return false };
     let methods = allocator_shim_contents(tcx, kind);
-    codegen_inner(tcx, module, &methods, tcx.sess.opts.unstable_opts.oom);
+    codegen_inner(tcx, module, &methods);
     true
 }
 
-fn codegen_inner(
-    tcx: TyCtxt<'_>,
-    module: &mut dyn Module,
-    methods: &[AllocatorMethod],
-    oom_strategy: OomStrategy,
-) {
+fn codegen_inner(tcx: TyCtxt<'_>, module: &mut dyn Module, methods: &[AllocatorMethod]) {
     let usize_ty = module.target_config().pointer_type();
 
     for method in methods {
@@ -65,35 +59,6 @@ fn codegen_inner(
         );
     }
 
-    {
-        let sig = Signature {
-            call_conv: module.target_config().default_call_conv,
-            params: vec![],
-            returns: vec![AbiParam::new(types::I8)],
-        };
-        let func_id = module
-            .declare_function(
-                &mangle_internal_symbol(tcx, OomStrategy::SYMBOL),
-                Linkage::Export,
-                &sig,
-            )
-            .unwrap();
-        let mut ctx = Context::new();
-        ctx.func.signature = sig;
-        {
-            let mut func_ctx = FunctionBuilderContext::new();
-            let mut bcx = FunctionBuilder::new(&mut ctx.func, &mut func_ctx);
-
-            let block = bcx.create_block();
-            bcx.switch_to_block(block);
-            let value = bcx.ins().iconst(types::I8, oom_strategy.should_panic() as i64);
-            bcx.ins().return_(&[value]);
-            bcx.seal_all_blocks();
-            bcx.finalize();
-        }
-        module.define_function(func_id, &mut ctx).unwrap();
-    }
-
     {
         let sig = Signature {
             call_conv: module.target_config().default_call_conv,