Mark loads from globals aligned and notrap.

Mark loads from globals generated by cton_wasm or by legalization as
`aligned` and `notrap`, since memory for these globals should be
allocated by the runtime environment for that purpose. This reduces
the number of potentially trapping instructions, which can reduce
the amount of metadata required by embedding environments.

lib/wasm/src/environ/dummy.rs

@@ -209,7 +209,10 @@ impl<'dummy_environment> FuncEnvironment for DummyFuncEnvironment<'dummy_environ
             let ext = pos.ins().uextend(I64, callee);
             pos.ins().imul_imm(ext, 4)
         };
-        let func_ptr = pos.ins().load(ptr, ir::MemFlags::new(), callee_offset, 0);
+        let mut mflags = ir::MemFlags::new();
+        mflags.set_notrap();
+        mflags.set_aligned();
+        let func_ptr = pos.ins().load(ptr, mflags, callee_offset, 0);
 
         // Build a value list for the indirect call instruction containing the callee, call_args,
         // and the vmctx parameter.