[PATCH] build: Fix multiple test failures with Clang and lld

[Joseph Myers]

On Fri, 26 Sep 2025, maozhao wrote:

>  /* Absolute value of X.  */
> +#if __GNUC_PREREQ (4, 9) || defined(__clang__)
> +/* Use a C11 _Generic implementation for Clang and modern GCC to provide
> +   better diagnostics and avoid false positives from -Wabsolute-value. This
> +   is a baseline implementation using only standard C types. */

<tgmath.h> needs to support the _FloatN and _FloatNx types.  An 
implementation ignoring them is not suitable.

If users building user programs with Clang get Clang's <tgmath.h> rather 
than glibc's, you shouldn't be putting workarounds in the installed header 
for the sake of glibc testing.  Rather, you should fix Clang's header to 
ensure it supports all the C23 features and GNU extensions that glibc's 
header does.

-- 
Joseph S. Myers
josmyers@redhat.com