[glibc] Fix failure when CFLAGS contains -DNDEBUG (Bug 25251)

[Carlos O'Donell <carlos@sourceware.org>]

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https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=83fe078130f62c35fcceab7133fa4b1512925951

commit 83fe078130f62c35fcceab7133fa4b1512925951
Author: Carlos O'Donell <carlos@redhat.com>
Date:   Tue Dec 3 15:42:24 2019 -0500

    Fix failure when CFLAGS contains -DNDEBUG (Bug 25251)
    
    Building tests with -DNDEBUG in CFLAGS, gcc 9.2.1 issues the following error:
    tst-assert-c++.cc: In function ‘int do_test()’:
    tst-assert-c++.cc:66:12: error: unused variable ‘value’ [-Werror=unused-variable]
       66 |     no_int value;
          |            ^~~~~
    tst-assert-c++.cc:71:18: error: unused variable ‘value’ [-Werror=unused-variable]
       71 |     bool_and_int value;
          |                  ^~~~~
    
    The assert has been disabled by building glibc with CFLAGS, CXXFLAGS,
    and CPPFLAGS with -DNDEBUG which removes the assert and leaves the
    value unused.
    
    We never want the assert disabled because that's the point of the
    test, so we undefine NDEBUG before including assert.h to ensure that
    we get assert correctly defined.

Diff:
---
 assert/tst-assert-c++.cc | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/assert/tst-assert-c++.cc b/assert/tst-assert-c++.cc
index 41cb487..c01fc8b 100644
--- a/assert/tst-assert-c++.cc
+++ b/assert/tst-assert-c++.cc
@@ -16,6 +16,9 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
+/* Undefine NDEBUG to ensure the build system e.g. CFLAGS/CXXFLAGS
+   does not disable the asserts we want to test.  */
+#undef NDEBUG
 #include <assert.h>
 
 /* The C++ standard requires that if the assert argument is a constant