[llvm] Update mibench to v1.

[ChrisCummins]

This deprecates the mibench-v0 dataset and adds a new mibench-v1
dataset. The difference is that the files in v1 have the "optnone"
attribute stripped, enabling the optimizer to modify the functions.

Fixes #505.

[codecov-commenter]

Codecov Report

Merging #511 (5aa5218) into development (87e4f7e) will decrease coverage by 0.14%.
The diff coverage is 100.00%.

@@               Coverage Diff               @@
##           development     #511      +/-   ##
===============================================
- Coverage        87.47%   87.33%   -0.15%     
===============================================
  Files              113      113              
  Lines             6397     6401       +4     
===============================================
- Hits              5596     5590       -6     
- Misses             801      811      +10     

Impacted Files	Coverage Δ
compiler_gym/envs/llvm/datasets/__init__.py	100.00% <100.00%> (ø)
compiler_gym/service/connection.py	77.02% <0.00%> (-2.37%)	⬇️
...loop_tool/service/loop_tool_compilation_session.py	86.57% <0.00%> (-2.02%)	⬇️

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