[Linux] [llvm] Fix LLVM symbol leakage to prevent conflict with other libs using LLVM like GLX

[archibate]

Related issue = fix #958

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By using libLLVM*.a, we not only export taichi::* in our libtaichi_core.so, but also export llvm::*.
So that some symbols in libLLVM-10.so (also llvm::*) somehow gets replaced by those one in libtaichi_core.so, which is our RTTI configured LLVM, causing the conflict.
So, this PR uses a LD version script, to prevent symbols in llvm::* being exported to global symbol table, therefore fix the leakage conflict, ultimately.

[yuanming-hu]

Cool! Thanks. Please feel free to merge as long as you can confirm the GLX issue presents without this PR but disappears with this PR.

[archibate]

Just BTW, does this fix the Blender compat issue which IIRC is related OpenGL?

[codecov]

Codecov Report

Merging #1508 into master will increase coverage by 0.46%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1508      +/-   ##
==========================================
+ Coverage   66.84%   67.31%   +0.46%     
==========================================
  Files          38       38              
  Lines        5450     5525      +75     
  Branches      956      966      +10     
==========================================
+ Hits         3643     3719      +76     
+ Misses       1644     1642       -2     
- Partials      163      164       +1     

Impacted Files	Coverage Δ
python/taichi/lang/matrix.py	91.33% <0.00%> (-0.10%)	⬇️
python/taichi/lang/transformer.py	93.82% <0.00%> (+0.20%)	⬆️
python/taichi/lang/ops.py	93.33% <0.00%> (+0.20%)	⬆️
python/taichi/main.py	42.35% <0.00%> (+0.28%)	⬆️
python/taichi/lang/__init__.py	80.00% <0.00%> (+0.53%)	⬆️

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