On loongarch, for example simde_mm_srai_epi16, GCC will generate
a vsrai.h instruction for '>>' operator if the imm8 is a real
immediate const value, otherwise it will generate two instructions
vsral.h and vreplgr2vr.h. But for clang it always generates two
instructions. So don't use intrinsics directly, instead let the
compiler itself to generate instructions based on imm8, which will
save one instruction for GCC at least.

Same for below:
simde_mm_srai_epi32
simde_mm_slli_epi[16/32/64]
simde_mm_srli_epi[16/32/64]
simde_mm256_slli_epi[16/32/64]
simde_mm256_srai_epi[16/32]
simde_mm256_srli_epi[16/32/64]