Update tests

src/test/ui/feature-gates/feature-gate-default_type_parameter_fallback.stderr

-error: defaults for type parameters are only allowed in `struct`, `enum`, `type`, or `trait` definitions.
+error: defaults for type parameters are only allowed in `struct`, `enum`, `type`, or `trait` definitions
   --> $DIR/feature-gate-default_type_parameter_fallback.rs:3:8
    |
 LL | fn avg<T=i32>(_: T) {}
@@ -8,7 +8,7 @@ LL | fn avg<T=i32>(_: T) {}
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #36887 <https://github.com/rust-lang/rust/issues/36887>
 
-error: defaults for type parameters are only allowed in `struct`, `enum`, `type`, or `trait` definitions.
+error: defaults for type parameters are only allowed in `struct`, `enum`, `type`, or `trait` definitions
   --> $DIR/feature-gate-default_type_parameter_fallback.rs:8:6
    |
 LL | impl<T=i32> S<T> {}

src/test/ui/generics/generic-non-trailing-defaults.rs

@@ -5,6 +5,5 @@
 
 struct Foo<A, B = Vec<C>, C>(A, B, C);
 //~^ ERROR generic parameters with a default must be trailing
-//~| ERROR generic parameters with a default cannot use forward declared identifiers
 
 fn main() {}

src/test/ui/panic-handler/weak-lang-item.stderr

@@ -10,10 +10,10 @@ help: you can use `as` to change the binding name of the import
 LL | extern crate core as other_core;
    |
 
-error: `#[panic_handler]` function required, but not found
-
 error: language item required, but not found: `eh_personality`
 
+error: `#[panic_handler]` function required, but not found
+
 error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0259`.