usage: ./build.sh [-x] [-a nt32|nt64] [-b debug|release] [-c] [-C] [-h]
                  [-i] [-n] [-N] [-r package[,...][:step]] [-t[.gz|.bz2|.xz]
                  [-v] [<target>[ ...]]
        -x                      Set the xtrace sh(1)ell option for debugging purposes.
        -a nt32|nt64            Selects 32-bit or 64-bit architecture; defaults to nt64.
        -b debug|release        Selects debug or release build; defaults to debug.
                                This currently only controls CFLAGS.
        -c                      Clean ${PREFIX} before processing build scripts.
        -C                      Check package(s) for updates upstream.
        -h                      Show this screen.
        -i                      Ignore SHA256 hash mismatches when downloading files.
        -n                      Perform dry run.
        -N                      Offline mode: no {wget,git-{clone,pull}}(1) calls.
        -r package[,...][:step] Restart the specified comma-separated build(s) completely or at
                                the optionally specified step. Currently defined steps are:
                                fetch extract build_dir patch_pre autoconf patch configure clean
                                build install.
        -t[.gz|.bz2|.xz]        Produce binary distribution and source tarballs containing ${PREFIX}
                                sans ${WORKDIR} and ${PREFIX}/src/midipix_build and ${WORKDIR} sans top-
                                level regular files at the end of a build with zero failures. The
                                tarballs will be compressed with either gzip, bzip2, or xz and signed
                                with GPG; the default compression is xz.
        -v                      Be verbose; this currently only affects secure_{cd,rm}() and insecure_mkdir().
        <target>[ ...]          One of:
                                host_toolchain, native_toolchain, runtime, lib_packages,
                                leaf_packages, world, or devroot.

        ${HOME}/midipix_build.vars, ../midipix_build.vars, and build.vars are sourced
        if they exist.

        Packages that are built by pkg.build will apply local patches in ${WORKDIR}
        named ${PKG_SUBDIR}.local.patch.

        Examples:
        ./build.sh -r coreutils
        Completely restart the coreutils build.

        ./build.sh -r coreutils:configure,build,install
        Restart the configure, build, and install steps of the coreutils build.

        ./build.sh -r psxscl GITROOT_HEAD=... PKG_PSXSCL_CFLAGS_CONFIGURE_EXTRA=-DPSX_INTERNAL_STRACE
        Build psxscl from the internal repository with strace enabled.

        ./build.sh -c -r ALL GITROOT_HEAD=...
        Clean ${PREFIX} and forcibly rebuild everything.

This script has been tested on the following platforms:
Alpine v3.4 (20160917_17:50) (x86_64)
Arch Linux 2016.02.01 (x86_64)
CentOS v7.2.1511 (Core) (x86_64)
Debian GNU/Linux v8.5 (stable) (jessie) (x86_64)
Exherbo Linux (x86_64-pc-linux-musl) (x86_64)
openSUSE 20150612 (Tumbleweed) (x86_64)