libstdc++: Combine two std::from_chars tests into one

We don't need separate tests for the C++17 and C++20 cases, we can just
have one test that uses __cpp_char8_t to adjust whether it tests char8_t
or not. This means the C++20 one doesn't fail if -fno-char8_t is used.

libstdc++-v3/ChangeLog:

	* testsuite/20_util/from_chars/1_neg.cc: Add char8_t cases,
	using a struct of that name if -fno-char8_t is active.
	* testsuite/20_util/from_chars/1_c++20_neg.cc: Removed.

2 files changed, 7 insertions, 43 deletions

diff --git a/libstdc++-v3/testsuite/20_util/from_chars/1_c++20_neg.cc b/libstdc++-v3/testsuite/20_util/from_chars/1_c++20_neg.cc
deleted file mode 100644
index d246eef..0000000
--- a/libstdc++-v3/testsuite/20_util/from_chars/1_c++20_neg.cc
+++ /dev/null
@@ -1,43 +0,0 @@
-// Copyright (C) 2017-2024 Free Software Foundation, Inc.
-//
-// This file is part of the GNU ISO C++ Library.  This library is free
-// software; you can redistribute it and/or modify it under the
-// terms of the GNU General Public License as published by the
-// Free Software Foundation; either version 3, or (at your option)
-// any later version.
-
-// This library is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
-// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-// GNU General Public License for more details.
-
-// You should have received a copy of the GNU General Public License along
-// with this library; see the file COPYING3.  If not see
-// <http://www.gnu.org/licenses/>.
-
-// { dg-do compile { target c++20 } }
-
-#include <charconv>
-
-void
-test01(const char* first, const char* last)
-{
-  wchar_t wc;
-  std::from_chars(first, last, wc); // { dg-error "no matching" }
-  std::from_chars(first, last, wc, 10); // { dg-error "no matching" }
-  char8_t c8;
-  std::from_chars(first, last, c8); // { dg-error "no matching" }
-  std::from_chars(first, last, c8, 10); // { dg-error "no matching" }
-  char16_t c16;
-  std::from_chars(first, last, c16); // { dg-error "no matching" }
-  std::from_chars(first, last, c16, 10); // { dg-error "no matching" }
-  char32_t c32;
-  std::from_chars(first, last, c32); // { dg-error "no matching" }
-  std::from_chars(first, last, c32, 10); // { dg-error "no matching" }
-  enum E { } e;
-  std::from_chars(first, last, e); // { dg-error "no matching" }
-  std::from_chars(first, last, e, 10); // { dg-error "no matching" }
-}
-
-// { dg-prune-output "enable_if" }
-// { dg-prune-output "cannot bind non-const lvalue reference" }
diff --git a/libstdc++-v3/testsuite/20_util/from_chars/1_neg.cc b/libstdc++-v3/testsuite/20_util/from_chars/1_neg.cc
index 7538d94..3f4cd59 100644
--- a/libstdc++-v3/testsuite/20_util/from_chars/1_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/from_chars/1_neg.cc
@@ -36,6 +36,13 @@ test01(const char* first, const char* last)
   enum E { } e;
   std::from_chars(first, last, e); // { dg-error "no matching" }
   std::from_chars(first, last, e, 10); // { dg-error "no matching" }
+
+#ifndef __cpp_char8_t
+  struct char8_t { };
+#endif
+  char8_t c8;
+  std::from_chars(first, last, c8); // { dg-error "no matching" }
+  std::from_chars(first, last, c8, 10); // { dg-error "no matching" }
 }
 
 // { dg-prune-output "enable_if" }