groups.d/231.native_packages_etc.group:{image,graphics}magick:${PKG_NO_PURGE_LA_FILES}: don't delete .la files.
    etc/README.md: documents NO_PURGE_LA_FILES.
    subr.pkg/pkg_install_files.subr:pkgp_install_files_libraries(): purge .la files subject to ${PKG_NO_PURGE_LA_FILES}.
    vars.env.d/000.build.env:${DEFAULT_BUILD_VARS}: adds NO_PURGE_LA_FILES.
    subr.ex/ex_rtl_rpm.subr:ex_rtl_purge_la_files(): removes duplicate function.