Build

Guard _DEFAULT_SOURCE against redefinition #61

Job	Run time
Debian (oldstable)	27s
macOS (macos-26)	10s
Debian (stable)	22s
Ubuntu (24.04 LTS)	28s
Rocky Linux 9	34s
Fedora (latest)	25s
macOS (macos-latest)	10s
openSUSE Leap	55s
Arch Linux	20s
Tag and release on version change	3s
Alpine (latest)	9s
Ubuntu (latest)	27s
	4m 30s

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