Rubyのエラー表示でbackslashがエスケープされる

$ docker run -it --rm rubylang/all-ruby env ALL_RUBY_SINCE=1.8 ./all-ruby -e "\\".foo
ruby-1.8.0            -e:1: undefined method `foo' for "\\":String (NoMethodError)
                  exit 1
...
ruby-1.8.7-p374       -e:1: undefined method `foo' for "\\":String (NoMethodError)
                  exit 1
ruby-1.9.0-0          -e:1:in `<main>': undefined method `foo' for "\\":String (NoMethodError)
                  exit 1
...
ruby-2.3.0-preview1   -e:1:in `<main>': undefined method `foo' for "\\":String (NoMethodError)
                  exit 1
ruby-2.3.0-preview2   -e:1:in `<main>': undefined method `foo' for "\\":String (NoMethodError)
                      Did you mean?  fork
                  exit 1
ruby-2.3.0            -e:1:in `<main>': undefined method `foo' for "\\":String (NoMethodError)
                  exit 1
...
ruby-2.6.0-rc2        -e:1:in `<main>': undefined method `foo' for "\\":String (NoMethodError)
                  exit 1
ruby-2.6.0            -e:1:in `<main>': undefined method `foo' for "\\":String (NoMethodError)
                      Did you mean?  for
                  exit 1
...
ruby-2.6.8            -e:1:in `<main>': undefined method `foo' for "\\":String (NoMethodError)
                      Did you mean?  for
                  exit 1
ruby-2.7.0-preview1   -e:1:in `<main>': undefined method `foo' for "\\\\":String (NoMethodError)
                      Did you mean?  for
                  exit 1
...
ruby-2.7.4            -e:1:in `<main>': undefined method `foo' for "\\\\":String (NoMethodError)
                      Did you mean?  for
                  exit 1
ruby-3.0.0-preview1   -e:1:in `<main>': undefined method `foo' for "\\\\":String (NoMethodError)
                  exit 1
...
ruby-3.0.2            -e:1:in `<main>': undefined method `foo' for "\\\\":String (NoMethodError)
                  exit 1

diff --git a/eval_error.c b/eval_error.c
index 98b8a22485..0b4a88ed52 100644
--- a/eval_error.c
+++ b/eval_error.c
@@ -103,10 +103,6 @@ write_warnq(VALUE out, VALUE str, const char *ptr, long len)
                     rb_write_error2(buf, snprintf(buf, sizeof(buf), "\\x%02X", c));
                 }
             }
-            else if (c == '\\') {
-                rb_write_error2(beg, ptr - beg + 1);
-                beg = ptr;
-            }
         }
         if (ptr > beg) {
             if (beg == RSTRING_PTR(str) && olen == RSTRING_LEN(str))