Auto merge of #894 - nivkner:fix_test, r=emilio

fix test for explicitly typed enum on aarch64

Fixes  #893

Author: bors-servo

tests/headers/enum_explicit_type.hpp

@@ -5,7 +5,7 @@ enum Foo: unsigned char {
     Qux
 };
 
-enum Neg: char {
+enum Neg: signed char {
     MinusOne = -1,
     One = 1,
 };