boost context suppoprt for mips64 support

[dixyes]

(Not so well) tested on loongson 3a4000 cpu

• Fixed architecture detect in config.m4
• Added new boost context code from boost context and "backported" it

在3a4000上（不是很完善地）测试过

• 修正了config.m4的架构判断
• 加入了boost context的新代码并且稍微backport了下来支持swoole使用的api

[codecov]

Codecov Report

Merging #4358 (a1a9063) into master (49e992e) will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4358      +/-   ##
==========================================
- Coverage   50.86%   50.84%   -0.03%     
==========================================
  Files          72       72              
  Lines       14610    14610              
==========================================
- Hits         7432     7429       -3     
- Misses       7178     7181       +3     

Impacted Files	Coverage Δ
src/os/msg_queue.cc	57.62% <0.00%> (-3.39%)	⬇️
src/os/async_thread.cc	68.85% <0.00%> (-0.88%)	⬇️
src/os/process_pool.cc	56.97% <0.00%> (-0.46%)	⬇️
src/network/client.cc	47.09% <0.00%> (+0.44%)	⬆️

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