Instead of adding MAKE_BOOTSTRAP for hosted environments, i.e., when
you want things simple, instead add MAKE_NATIVE to get those hugely
important features like __RCSID().
Also, get rid of a now-unneeded -I.
value for _PATH_DEFSHELLDIR. In theory, _PATH_DEFSHELLDIR will also be
used to find csh, but ".SHELL csh" shouldn't be used anywhere in our source
tree, and this make shouldn't be used for other things.
This should cause nbmake to use the right shell for most purposes when
cross-compiling from Solaris.
ross