Fixes for LoongArch LSX + fast math

[iv-m]

Fix a couple of errors I found when testing current simde master on my loongarch64 machine with GCC 14.3.1 and -Ofast -mlsx -mlasx in CFLAGS and CXXFLAGS.

[iv-m]

@HecaiYuan, @mr-c, please take a look.

[mr-c]

Thank you for the PR, @iv-m ; please address the issues at https://github.com/simd-everywhere/simde/actions/runs/21027953168/job/60456937165?pr=1369

[iv-m]

Please address the issues at [...]

Well, I just submitted fixes for two of the most obvious issues I found(

Other issues require more investigation. For example, the error from the CI:

 ../test/x86/avx512/../../../simde/x86/sse2.h: In function ‘simde_mm_cvtps_epi32’:
../test/x86/avx512/../../../simde/x86/sse2.h:3316:7: note: use ‘-flax-vector-conversions’ to permit conversions between vectors with differing element types or numbers of subparts
 3316 |       r_.lsx_i32 = __lsx_vftintrne_w_s(a_.lsx_f32);
      |       ^~
../test/x86/avx512/../../../simde/x86/sse2.h:3316:20: error: incompatible types when assigning to type ‘v4i32’ from type ‘__m128i’
 3316 |       r_.lsx_i32 = __lsx_vftintrne_w_s(a_.lsx_f32);
      |                    ^~~~~~~~~~~~~~~~~~~

It looks like GCC bug to me: __lsx_vftintrne_w_s, as far as I can know, returns four 32-bit integers packed into __m128, but GCC 14 for some reason thinks otherwise.

I'm not sure I'm qualified enough and have time to address all the issues there rn. I probably can disable the preporcessor branches for optimizations that break CI -- that's more or less what I did for my local simde copy -- and hope that LoongArch community (me included) will eventually implement them back. If this is the way to go, what is the preferred conventions for that? Something along the lines of #if 0 && ... or just plane removal?

[mr-c]

If this is the way to go, what is the preferred conventions for that?

Please file issues with GCC, then we can add a entry near

simde/simde/simde-common.h

Line 1058 in 613c365

# if defined(SIMDE_ARCH_POWER)

to define SIMDE_BUG_GCC_NNNN only for circumstances where it is active.

Then we can add && !defined(SIMDE_BUG_GCC_NNNN) to

simde/simde/x86/sse2.h

Line 3314 in 613c365

#elif defined(SIMDE_LOONGARCH_LSX_NATIVE) && defined(SIMDE_FAST_CONVERSION_RANGE) && defined(SIMDE_FAST_ROUND_TIES)

You can also experiment with adding cast using HEDLEY_REINTERPRET_CAST if you'd like to use this function before a fix is released for GCC