build initramfs: uncontrolled LD_LIBRARY_PATH

[John Reiser <jreiser-Po6cBsTGB2ZWk0Htik3J/w@public.gmane.org>]

dracut uses ldd when building an initramfs, but I cannot find where
dracut controls LD_LIBRARY_PATH during the build.  Thus I do not trust
the results of ldd.  The string "LD_LIBRARY_PATH" does not appear
in the dracut source tree, there is no use of "env -i", dracut is
not setuid, etc.

At a minimum, the built initramfs could fail to satisfy some DT_NEEDED
entry during boot, leading to a crash.  Some soname was satisfied by
a library in a non-standard directory on the build-time LD_LIBRARY_PATH,
and was copied into that non-standard directory of the initramfs, but is
not findable using the boot-time (default standard) path list.

That might be the worst, because all users of the initramfs (namely:
booting only) do control LD_LIBRARY_PATH, so there might be "no possibility"
of substituting an actual non-standard library.  However, it would be
safer to control LD_LIBRARY_PATH while building initramfs, or at least
document why not.

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