Fix syntax error

Author: Amanieu

src/libpanic_unwind/seh.rs

@@ -218,7 +218,7 @@ extern "C" {
 // an argument to the C++ personality function.
 //
 // Again, I'm not entirely sure what this is describing, it just seems to work.
-#[cfg_attr(bootstrap(msvc_try_filter))]
+#[cfg_attr(bootstrap, lang = "msvc_try_filter")]
 #[cfg_attr(not(any(test, bootstrap)), lang = "eh_catch_typeinfo")]
 static mut TYPE_DESCRIPTOR: _TypeDescriptor = _TypeDescriptor {
     pVFTable: unsafe { &TYPE_INFO_VTABLE } as *const _ as *const _,