This function tries to determine the appropriate Rust target for this
instance of R. Or, it gives the targets necessary for CRAN build machines.
Usage
target(cran = FALSE)
Arguments
cran
Are targets for all CRAN build machines desired?
Value
If cran=FALSE, a string giving a Rust target, or "" if
this cannot be determined. If cran=TRUE, a character vector giving
the targets necessary for CRAN build machines.