libschedutil: use preprocessor symbols for flags #2504

Job	Run time
python linting	33s
Generate build matrix	7s
validate commits	0s
spelling	6s
bookworm - test-install	10m 21s
bookworm - 32 bit	10m 20s
noble - test-install	10m 20s
el9 - test-install	10m 20s
alpine - test-install	10m 20s
fedora40 - test-install	10m 19s
jammy - test-install	10m 19s
focal - py3.8	10m 17s
bookworm - gcc-12,content-s3,distcheck	10m 19s
fedora40 - clang-18	10m 18s
coverage	10m 18s
el8 - ascii	10m 18s
el8 - test-install	10m 18s
el8 - system,coverage	7m 30s
inception	10m 17s
flux-pmix check	9m 50s
flux-sched check	6m 51s
flux-accounting check	4m 38s
macos build only	2m 55s
flux-pam check	4m 14s
Generate docker manifest	1s
	3h 1m 9s

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