propagate revert data when external call fails

[charles-cooper]

What I did

Fix #2529

How I did it

Change straight assert (call ...) to

if !(call ...) (seq
(returndatacopy 0 0 returndatasize)
(revert 0 returndatasize)
))

How to verify it

Check out tests

Description for the changelog

Propagate revert data when external call fails

Cute Animal Picture

[codecov-commenter]

Codecov Report

Merging #2531 (b9e1dbc) into master (9a5dd50) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #2531   +/-   ##
=======================================
  Coverage   84.67%   84.68%           
=======================================
  Files          93       93           
  Lines        9301     9306    +5     
  Branches     2096     2096           
=======================================
+ Hits         7876     7881    +5     
  Misses        940      940           
  Partials      485      485           

Impacted Files	Coverage Δ
vyper/builtin_functions/functions.py	88.62% <100.00%> (ø)
vyper/old_codegen/external_call.py	94.33% <100.00%> (ø)
vyper/old_codegen/parser_utils.py	83.01% <100.00%> (+0.23%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 9a5dd50...b9e1dbc. Read the comment docs.