Use C++14 for TF 2.7

[njzjz]

No description provided.

[codecov-commenter]

Codecov Report

Merging #1275 (7475193) into devel (4e15b0d) will increase coverage by 11.69%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##            devel    #1275       +/-   ##
===========================================
+ Coverage   64.28%   75.97%   +11.69%     
===========================================
  Files           5       91       +86     
  Lines          14     7406     +7392     
===========================================
+ Hits            9     5627     +5618     
- Misses          5     1779     +1774     

Impacted Files	Coverage Δ
deepmd/utils/errors.py	100.00% <0.00%> (ø)
source/op/_prod_force_se_r_grad.py	100.00% <0.00%> (ø)
deepmd/utils/type_embed.py	100.00% <0.00%> (ø)
deepmd/__about__.py	0.00% <0.00%> (ø)
deepmd/train/run_options.py	86.79% <0.00%> (ø)
deepmd/entrypoints/train.py	87.64% <0.00%> (ø)
deepmd/entrypoints/compress.py	76.36% <0.00%> (ø)
deepmd/utils/batch_size.py	96.00% <0.00%> (ø)
deepmd/utils/__init__.py	100.00% <0.00%> (ø)
deepmd/utils/weight_avg.py	20.00% <0.00%> (ø)
... and 76 more

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