Optionally disable caching allocator

[hkaiser]

No description provided.

[codacy-production]

Coverage summary from Codacy

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Coverage variation	Diff coverage
Report missing for 3253ee11	94.87%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (3253ee1)	Report Missing	Report Missing	Report Missing
Head commit (8530848)	189610	161581	85.22%

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#6393)	39	37	94.87%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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[NK-Nikunj]

https://github.com/STEllAR-GROUP/hpx/pull/6393/files#diff-bd1f43d73c88a8bdda46746af0e6bcdb9612ac716943cdc86a272028e326fc5dR116

Why use std::stack here when the operators involved in thread cache is the equivalent of a push_back and a pop_back? A std::vector should be better pick, no?

[hkaiser]

https://github.com/STEllAR-GROUP/hpx/pull/6393/files#diff-bd1f43d73c88a8bdda46746af0e6bcdb9612ac716943cdc86a272028e326fc5dR116

Why use std::stack here when the operators involved in thread cache is the equivalent of a push_back and a pop_back? A std::vector should be better pick, no?

Does it make a difference? But sure, please feel free to create a PR for this.