stdlib: Add testcases for abs(). (BZ #30263)

Test minimum and maximum int values, zero, and part of the range
of int values.  Use '-fno-builtin' to ensure we are testing the
implementation.

Reviewed-by: Wilco Dijkstra  <Wilco.Dijkstra@arm.com>

stdlib/Makefile

@@ -184,6 +184,7 @@ tests := \
   testmb2 \
   testrand \
   testsort \
+  tst-abs \
   tst-arc4random-fork \
   tst-arc4random-stats \
   tst-arc4random-thread \
@@ -287,6 +288,8 @@ LDLIBS-test-dlclose-exit-race = $(shared-thread-library)
 LDFLAGS-test-dlclose-exit-race = $(LDFLAGS-rdynamic)
 LDLIBS-test-dlclose-exit-race-helper.so = $(libsupport) $(shared-thread-library)
 
+CFLAGS-tst-abs.c += -fno-builtin
+
 ifeq ($(have-cxx-thread_local),yes)
 CFLAGS-tst-quick_exit.o = -std=c++11
 LDLIBS-tst-quick_exit = -lstdc++

stdlib/tst-abs.c

@@ -0,0 +1,45 @@
+/* Basic tests for abs.
+   Copyright (C) 2023 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
+   <https://www.gnu.org/licenses/>.  */
+
+#include <limits.h>
+#include <stdlib.h>
+
+#include <support/check.h>
+
+#define LARGE_PRIME 49999
+
+static int do_test (void)
+{
+  int i;
+
+  TEST_COMPARE(abs(INT_MAX), INT_MAX);
+  TEST_COMPARE(abs(INT_MIN + 1), INT_MAX);
+  TEST_COMPARE(abs(-1), 1);
+  TEST_COMPARE(abs(0), 0);
+  TEST_COMPARE(abs(1), 1);
+
+  for (i = INT_MIN + 1; i < 0; i += LARGE_PRIME)
+    TEST_COMPARE(abs(i), -i);
+
+  for (i = 0; i < INT_MAX - LARGE_PRIME; i += LARGE_PRIME)
+    TEST_COMPARE(abs(i), i);
+
+  return EXIT_SUCCESS;
+}
+
+#include <support/test-driver.c>