support: Introduce new subdirectory for test infrastructure

The new test driver in <support/test-driver.c> has feature parity with
the old one.  The main difference is that its hooking mechanism is
based on functions and function pointers instead of macros.  This
commit also implements a new environment variable, TEST_COREDUMPS,
which disables the code which disables coredumps (that is, it enables
them if the invocation environment has not disabled them).

<test-skeleton.c> defines wrapper functions so that it is possible to
use existing macros with the new-style hook functionality.

This commit changes only a few test cases to the new test driver, to
make sure that it works as expected.

support/check.h

@@ -0,0 +1,49 @@
+/* Macros for reporting test results.
+   Copyright (C) 2016 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef SUPPORT_CHECK_H
+#define SUPPORT_CHECK_H
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+/* Print failure message to standard output and return 1.  */
+#define FAIL_RET(...) \
+  return support_print_failure_impl (__FILE__, __LINE__, __VA_ARGS__)
+
+/* Print failure message and terminate the process with STATUS.  */
+#define FAIL_EXIT(status, ...) \
+  support_exit_failure_impl (status, __FILE__, __LINE__, __VA_ARGS__)
+
+/* Print failure message and terminate with exit status 1.  */
+#define FAIL_EXIT1(...) \
+  support_exit_failure_impl (1, __FILE__, __LINE__, __VA_ARGS__)
+
+int support_print_failure_impl (const char *file, int line,
+                                const char *format, ...)
+  __attribute__ ((nonnull (1), format (printf, 3, 4)));
+void support_exit_failure_impl (int exit_status,
+                                const char *file, int line,
+                                const char *format, ...)
+  __attribute__ ((noreturn, nonnull (2), format (printf, 4, 5)));
+
+
+__END_DECLS
+
+#endif /* SUPPORT_CHECK_H */