svm: optimize local program cache creation

[2501babe]

TODO part 2 of #4680

this works. just needs cleanup and confirmation it achieves its perf goals

Problem

Summary of Changes

Fixes #

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 97.38220% with 10 lines in your changes missing coverage. Please review.

Project coverage is 82.9%. Comparing base (44bd7c7) to head (03dc7f4).
Report is 21 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##           master    #4697     +/-   ##
=========================================
- Coverage    83.0%    82.9%   -0.1%     
=========================================
  Files         828      828             
  Lines      375869   375986    +117     
=========================================
- Hits       312178   312067    -111     
- Misses      63691    63919    +228     

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[2501babe]

superceded, hopefully once and for all, by #6036