[PATCH] Add a comment for NO_MATH_REDIRECT

[DJ Delorie]

Could you two please decide which of you is going to own this comment?  ;-)

https://patchwork.sourceware.org/project/glibc/patch/20251028171141.3208834-10-adhemerval.zanella@linaro.org/
Adhemerval's v2 "math: Don't redirect inlined builtin math functions" proposes:
>  /* NB: Internal tests don't have access to internal symbols.  */
>  # if !IS_IN (testsuite_internal) \
>       && !(defined __FINITE_MATH_ONLY__ && __FINITE_MATH_ONLY__ > 0)
> +/* NB: Do not redirect math builtin functions when they are inlined.  */
> +# include <math-use-builtins.h>
>  #  ifndef NO_MATH_REDIRECT
>  /* Declare some functions for use within GLIBC.  Compilers typically
>     inline those functions as a single instruction.  Use an asm to

https://patchwork.sourceware.org/project/glibc/patch/CAMe9rOr9HpwZuXy0j5v05pGDFULKR1K6DvDN=5C2O+uJrDhDig@mail.gmail.com/
"H.J. Lu" <hjl.tools@gmail.com> proposes:
>  /* NB: Internal tests don't have access to internal symbols.  */
>  # if !IS_IN (testsuite_internal) \
>       && !(defined __FINITE_MATH_ONLY__ && __FINITE_MATH_ONLY__ > 0)
> +/* NO_MATH_REDIRECT must be defined in the source implementing function,
> +   FUNC, if FUNC is implemented as an alias of __FUNC or vice versa to
> +   avoid redirecting FUNC to __FUNC.  */
>  #  ifndef NO_MATH_REDIRECT
>  /* Declare some functions for use within GLIBC.  Compilers typically
>     inline those functions as a single instruction.  Use an asm to

https://patchwork.sourceware.org/project/glibc/patch/20251031200300.3716090-7-adhemerval.zanella@linaro.org/
Adhemerval's v3 proposes:
>  /* NB: Internal tests don't have access to internal symbols.  */
>  # if !IS_IN (testsuite_internal) \
>       && !(defined __FINITE_MATH_ONLY__ && __FINITE_MATH_ONLY__ > 0)
> +/* NO_MATH_REDIRECT must be defined in the source implementing function,
> +   FUNC, if FUNC is implemented as an alias of __FUNC or vice versa to
> +   avoid redirecting FUNC to __FUNC.  */
> +#  include <math-use-builtins.h>
> +/* NB: Do not redirect math builtin functions when they are inlined.  */
>  #  ifndef NO_MATH_REDIRECT
>  /* Declare some functions for use within GLIBC.  Compilers typically
>     inline those functions as a single instruction.  Use an asm to