printf -v is not available in some shells

[sparr]

There are four instances of printf -v in funclib.sh (e.g. https://github.com/gnulib-modules/bootstrap/blob/master/build-aux/funclib.sh#L1156) which do not work in the dash shell. Although that file doesn't specify #!/bin/sh, the bootstrap script it ends up included in does. These printf -v var ... should be replaced with var="$(printf ...)" which will allow the tests in question to proceed on dash and potentially get a faster func_quotefast_eval than the fallback.

See: https://salsa.debian.org/debian/devscripts/-/blob/main/scripts/checkbashisms.pl?ref_type=heads#L706 (against which I'll be submitting a patch about the quoting shortly)