Fix zlib handling in stdenvLinux

Previously stdenv depended on two different zlibs and there was a third
one in the top-level package set for other purposes.  This commit merges
all this zlibs to one.
GCC >= 4.8 doesn't depend on ppl
ed: update to 1.10 (close #3852)
Use the new allowedRequisites feature in stdenvLinux

This way we properly check that the end-result stdenv of the quite
complicated multistage stdenvLinux building procedure is sane, and only
depends on the stuff that we know about.

Alternative would be to just disallowRequisites bootstrapTools, which is
the most common offender, but we have had other offenders in the past.