time: Make gmtime_r() visible to Zephyr #128

Job	Run time
cache-maker	8m 58s
release-zephyr (./.github/do-zephyr)	32m 25s
minsize-zephyr (./.github/do-zephyr)	31m 50s
release-zephyr (-Dio-float-exact=false -Dio-long-long=true -Dio-percent-b=true -Dio-long-double=t...	32m 30s
minsize-zephyr (-Dio-float-exact=false -Dio-long-long=true -Dio-percent-b=true -Dio-long-double=t...	32m 17s
release-zephyr (-Dformat-default=integer -Dfreestanding=true -Dposix-io=false -Dnewlib-obsolete-m...	32m 18s
minsize-zephyr (-Dformat-default=integer -Dfreestanding=true -Dposix-io=false -Dnewlib-obsolete-m...	32m 17s
release-zephyr (-Dtinystdio=false, ./.github/do-zephyr)	16m 19s
minsize-zephyr (-Dtinystdio=false, ./.github/do-zephyr)	15m 43s
release-zephyr (-Dtinystdio=false -Dnewlib-io-float=true -Dio-long-long=true -Dio-long-double=tru...	15m 51s
minsize-zephyr (-Dtinystdio=false -Dnewlib-io-float=true -Dio-long-long=true -Dio-long-double=tru...	15m 6s
	4h 25m 34s

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