gen_initramfs: add /sbin/ldconfig to the initramfs

ldconfig will allow us to create ld.so.cache at runtime, if needed
linuxrc: create /etc/ld.so.cache if it's not in the initramfs
gen_initramfs.sh: use realpath to ensure that udevdir files are grepped correctly

See Gentoo bug #495194
tar refuses to extract into a non-existent directory

This helps if trying to use a new directory as the temporary directory.
LVM has read-only files that would prompt for deletion

This only happens when testing as a non-root user, but even so, it
doesn't hurt to make this less annoying.
NO_KERNEL_SOURCES left behind

This looks like a leftover from a141d71531669dc888911c9141fd98ade753d200.

All occurrences of NO_KERNEL_SOURCES should have been replaced by
the negated KERNEL_SOURCES.

Though probably isTrue should be used for all boolean options, to avoid
confusion when setting them in the config file (some of them should be
set to 0 or 1, while others support yes/no/0/1/true/false).
Fix a typo LCV -> LOV
Fix the kerncache parsing of CONFIG_LOCALVERSION

A couple of problems here.

1. CONFIG_LOCALVERSION was never added the kerncache.config.
2. Parsing of CONFIG_LOCALVERSION expects kernel .config style syntax.
   For this point I opted for the extra space, to make the
   kerncache.config syntax consistent. There is no good reason to even
   keep the CONFIG_LOCALVERSION name.
Trying to build a binary package, so leave the system alone

Trying to build everything (and package it in a pbin) as a non-root user, so
leave the filesystem alone.
ldconfig -r requires "root" (chroot) privileges

This would not do the right thing when running as a non-root user but
anyone running this as non-root should be aware that things could break.
Also detect "fakeroot"
Only skip the "ldconfig -r" step, which needs root privileges

Since we now have ldconfig which can run during the boot, make sure we
unconditionally copy all the other configuration files (ld.so.conf and
relatives), while only skipping the "cache" step.