update: untap/retap formulae before/after pull.

This should fix problems like #19799 where we pull formulae from taps
into core. I want to get something similar merged ASAP so we can pull
GCC into core (see #20678).

Closes #19799.
update: handle realpath exception.
Remove formulae moved to homebrew-science
gdal: optional netcdf dep is in homebrew-science
gmp: add bottles.
isl: add bottles.
cloog: add bottles.