Fixed _mm256_set_m128 is only availble on gcc8+. issue#5072

[whyb]

Fixed _mm256_set_m128 is only availble on gcc8+. issue #5072

[tencent-adm]

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1 out of 2 committers have signed the CLA.

✅ nihui
❌ whyb
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[codecov-commenter]

Codecov Report

Merging #5075 (643816e) into master (75ad1cc) will decrease coverage by 0.01%.
Report is 2 commits behind head on master.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #5075      +/-   ##
==========================================
- Coverage   94.73%   94.73%   -0.01%     
==========================================
  Files         767      767              
  Lines      230160   230161       +1     
==========================================
  Hits       218049   218049              
- Misses      12111    12112       +1     

Files	Coverage Δ
src/layer/x86/shufflechannel_x86.cpp	97.51% <100.00%> (+<0.01%)	⬆️

... and 1 file with indirect coverage changes

[nihui]

Thanks for your contribution !