Log Message:
(devel/R-pkgbuild) Updated 1.4.0 to 1.4.1

# pkgbuild 1.4.1

* New `Config/build/extra-sources` `DESCRIPTION` option to make pkgbuild aware
  of extra source files to consider in `needs_compile()`.

* New `Config/build/bootstrap` `DESCRIPTION` option. Set it to `TRUE` to run
  `Rscript bootstrap.R` in the package root prior to building the source
  package (#157, @paleolimbot).

* pkgbuild now supports Rtools43.

* pkgbuild now always _appends_ its extra compiler flags to the ones that
  already exist in the system and/or user `Makevars` files (#156).