FStarC.Util: make sure executable_name and exec_dir point to concrete… #192

Job	Run time
build / build	19m 34s
nix / fstar-nix	18m 18s
tests / test-local	15m 13s
tests / check-stage3	6m 12s
tests / ocaml-smoke (fstar-src.tar.gz, ubuntu-20.04)	7m 43s
tests / binary-smoke (fstar.tar.gz, ubuntu-24.04)	17s
tests / perf-canaries	13s
tests / ocaml-smoke (fstar-src.tar.gz, ubuntu-22.04)	7m 42s
tests / ocaml-smoke (fstar-src.tar.gz, ubuntu-latest)	7m 53s
ciok	1s
	1h 23m 6s

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