Glibc 2.42+ conflicts with `rsqrt`/`rsqrtf` defs in `builtins.h`

[griffi-gh]

Noticed this while working on Nix packaging

As of glibc 2.42 (?? apparently), rsqrt/rsqrtf are declared in <bits/mathcalls.h> (include'd by both <math.h> and <cmath>)

SCALE's redscale_impl/builtins.h unconditionally includes and declares its own rsqrt(double), the two now conflict:

error: __host__ function 'rsqrt' cannot overload __host__ __device__ function 'rsqrt'

I had to comment those defs out from redscale_impl/builtins.h for the build to proceed:

__host__ __DEVICE float rsqrt(float);
__host__ __DEVICE double rsqrt(double);
__host__ __DEVICE float rsqrtf(float);

[griffi-gh]

NOTE: opensubdiv seemingly affected by the same issue, with sinpif conflicting this time:

       > /nix/store/q5wv2ldpcv5w8yb2wmsngsygvlxb73fk-glibc-2.42-67-dev/include/math.h:295:34: note: expanded from macro '__MATH_PRECNAME'
       >   295 | # define __MATH_PRECNAME(name,r) name##f##r
       >       |                                  ^
       > <scratch space>:158:1: note: expanded from here
       >   158 | sinpif
       >       | ^
       > /nix/store/bdqb1wj377wv6gnjkbvzz9yba7ivbjwc-scale-nvcc-0-unstable-2026.07.12/include/redscale_impl/builtins.h:691:16: note: previous declaration is here
       >   691 | __host__ float sinpif(float);
       >       |                ^
       > 2 errors generated when compiling for host.

[griffi-gh]

glibc 2.42 added the C23 sinpi cospi tanpi asinpi acospi atanpi atan2pi definitions as well which also conflict
(they are noexcept unlike the SCALE variants)