vars/{build,env}.vars: diet, pt. II.
    vars/build.vars: install w/ `DESTDIR=<prefix> PREFIX= prefix=' by default.
    vars/build.vars:cmake: build w/ -g0 -O2.
    vars/cmake.vars: build using cmake_host.
    vars/pkgconf_host.vars: remove & don't install ${PREFIX}/bin/pkg-config link to avoid confusing host packages.
    vars/{apr_util,chainport}.vars: replaced w/ corresponding ${PKG_BUILD_STEPS}.
    patches/perl-5.22.1.local.patch: pass -L. -lperl when linking.
    patches/smallbasic.local.patch: don't call pcre-config.
    subr/pkg_autoconf.subr, vars/{lib{caca,udns},toilet}.vars: always install config.sub after bootstrap.
    subr/pkg_disabled.subr: always silently finish disabled packages.
    subr/pkg_setup_{env,vars}.subr: split.
    subr/pkg_{build,install}.subr: always pass LIBTOOL=${PKG_SLIBTOOL:=slibtool}.
    subr/pkg_{{build,work}_dir,extract,setup_env}.subr: infer ${PKG_BUILD_DIR} from ${PKG_SUBDIR} given the absence of configure{,.{ac,in}}.