Various packages under minimal-bootstrap explicitly use the musl gcc
wrapper (especially the *-static packages).
In #494106, the desire is to allow these packages to run on a host
platform which may differ from the bootstrap seed platform. That host
platform may be a non-musl platform, and furthermore musl may not even
be available on the desired host architecture.
This change aims to make the packages more generic wrt libc. It is
extracted out of #494106.
Adds --enable-checking=release and --disable-{libgomp,libquadmath,libitm,libvtv,libssp,libatomic,libstdcxx-pch,nls} to all GCCs (those runtime libs are unused by the stdenv); switches gcc-4.6{,cxx} to install-strip; adds --disable-nls to binutils and coreutils; adds --disable-test-modules --without-ensurepip --without-static-libpython to python.
Bootstrap self-size 1.45 GB -> 940 MB; gcc46-cxx -14%, glibc -10%, gcc-latest -6% wall on the heavy builds.
(make -j was tried on tcc-built derivations and broke them silently; NOTE comments left in the affected files so this isn't re-attempted.)
