Remove -march for riscv

[Hamlin-Li]

Hi, Can you review this simple change? It removes the -march argument when cross-compile riscv in make_so_cross.sh. This is to let the compiler to pick up the default arch, to enable most compatability on different hardwares. Thanks!

[codecov-commenter]

Codecov Report

Merging #283 (f327725) into master (1ab2d21) will decrease coverage by 0.15%. The diff coverage is n/a.

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@@             Coverage Diff              @@
##             master     #283      +/-   ##
============================================
- Coverage     59.88%   59.74%   -0.15%     
+ Complexity      302      301       -1     
============================================
  Files            26       26              
  Lines          1421     1421              
  Branches        164      164              
============================================
- Hits            851      849       -2     
- Misses          416      417       +1     
- Partials        154      155       +1     

[luben]

LGTM

[Hamlin-Li]

Thanks for your reviewing.