- Followup to <ffcc9c6a9dfeb481fb342accb71579ae5478ea74>.
    - Fix pseudo-local variable leaks in build.subr.
    - Log $PKG_* environment variables prior to building w/ pkg.build.
    - Always build musl w/ -g2 -O0.
    - Remove obsolete export CFLAGS=${CFLAGS_LVL${BUILD_LVL}} command from build.sh.
    - Handle bin/libpsxscl.{last,log} in midipix.sh.
    - Add autoconf to $CHECK_PREREQ_CMDS.
    - Include `Create `Midipix mintty shell' shortcut.vbs' in the tarball.
    - Changes the $PKG_ENV_VARS_EXTRA variable name-value pair separator from `,' to `:'.
    - Link bash and coreutils statically.
    - Changes the level 2 package --prefix to `', installing to DESTDIR=$PREFIX_LVL2.