that broke a case where we had -DMISC=$(call gb_Helper_conver_native,...)
which transformed in to -DMISC=   d:/foo/bar
and broke the build

otherwise we construct file like d://libo/... which break stuf

only PATH and SOLARENV which is used as a trigger to call Env.Host.sh
are left...

JAVAHOME is used in an obscure test module in moz, that does not seems
to be run anyway... other than that, no trace of it
so no need to export it.

prep-work for the migration of PATH handling from set_soenv...