[PATCH v4] Fix failure when CFLAGS contains -DNDEBUG (Bug 25251)

[Florian Weimer]

* Carlos O'Donell:

> 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.
> ---
>  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 41cb487512..c01fc8bd25 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

Looks good to me.

Thanks,
Florian