Nuke chflags on LIB32TMP and WORLDTMP

Sometimes these directories can be chflag'ed noschg, which means that
the rm -rf will fail immediately; just unchflag the entire directory
like cleanworld does today.

Signed-off-by: Garrett Cooper <yanegomi@gmail.com>
Instead of specially filtering out lib/pam, use the commands macro
to determine whether or not a rule should be generated.

Signed-off-by: Garrett Cooper <yanegomi@gmail.com>
Allow user to specify _prebuild_libs via LOCAL_PREBUILD_LIB_DIRS

Sometimes LOCAL_LIB_DIRS depends on libraries not available in
_prebuild_libs, so it's necessary to tack on libraries in this
way to avoid running into build/linker errors later on.

Signed-off-by: Garrett Cooper <yanegomi@gmail.com>