Make oom-heap.c test work with newer GCC

[SvizelPritula]

This pull request fixes the oom-heap (C11 / gcc) test.

New GCC versions can optimize the old version of the test to use practically zero memory.

[codecov-commenter]

Codecov Report

Merging #40 (61591f0) into old-master (1afb72a) will increase coverage by 0.00%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           old-master      #40   +/-   ##
===========================================
  Coverage       63.60%   63.60%           
===========================================
  Files             234      234           
  Lines           17278    17278           
===========================================
+ Hits            10989    10990    +1     
+ Misses           6289     6288    -1     

Flag	Coverage Δ
functionaltests	47.25% <ø> (-0.13%)	⬇️
unittests	44.14% <ø> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
cms/service/esoperations.py	80.55% <0.00%> (-3.48%)	⬇️
cms/db/util.py	53.33% <0.00%> (-2.97%)	⬇️
cms/service/ScoringService.py	67.64% <0.00%> (-2.95%)	⬇️
cms/io/PsycoGevent.py	57.14% <0.00%> (-2.86%)	⬇️
cms/grading/scoring.py	75.58% <0.00%> (-2.33%)	⬇️
cms/io/rpc.py	92.66% <0.00%> (-1.34%)	⬇️
cms/db/base.py	87.12% <0.00%> (-1.00%)	⬇️
cms/db/filecacher.py	79.14% <0.00%> (-0.93%)	⬇️
cms/io/service.py	73.41% <0.00%> (-0.64%)	⬇️
cms/server/contest/handlers/tasksubmission.py	49.20% <0.00%> (-0.53%)	⬇️
... and 11 more

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