Re-use free space in executable pages across asm blocks

[twitchyliquid64]

I had forgotten to go back and do this.

This simply re-uses free space in a executable page this should greatly improve memory utilization & also improve locality a bit.

[codecov-io]

Codecov Report

Merging #126 into master will increase coverage by 0.05%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #126      +/-   ##
==========================================
+ Coverage   66.55%   66.61%   +0.05%     
==========================================
  Files          41       41              
  Lines        4246     4253       +7     
==========================================
+ Hits         2826     2833       +7     
  Misses       1149     1149              
  Partials      271      271

Impacted Files	Coverage Δ
exec/internal/compile/allocator.go	86.2% <100%> (+4.38%)	⬆️

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