tinystdio: ungetc decrements file position indicator correctly #20

Job	Run time
cache-maker	9s
minsize-zephyr (./.github/do-zephyr)	36m 40s
release-zephyr (./.github/do-zephyr)	37m 40s
minsize-zephyr (-Dio-float-exact=false -Dio-long-long=true -Dio-percent-b=true -Dio-long-double=t...	36m 16s
release-zephyr (-Dio-float-exact=false -Dio-long-long=true -Dio-percent-b=true -Dio-long-double=t...	37m 15s
minsize-zephyr (-Dformat-default=integer -Dfreestanding=true -Dposix-io=false -Dnewlib-obsolete-m...	36m 50s
release-zephyr (-Dformat-default=integer -Dfreestanding=true -Dposix-io=false -Dnewlib-obsolete-m...	37m 30s
minsize-zephyr (-Dtinystdio=false, ./.github/do-zephyr)	21m 19s
minsize-zephyr (-Dtinystdio=false -Dnewlib-io-float=true -Dio-long-long=true -Dio-long-double=tru...	12m 49s
release-zephyr (-Dtinystdio=false, ./.github/do-zephyr)	22m 19s
release-zephyr (-Dtinystdio=false -Dnewlib-io-float=true -Dio-long-long=true -Dio-long-double=tru...	12m 24s
	4h 51m 11s

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