Makefile.in (AS_FOR_TARGET, [...]): Don't use double quotes to avoid quotes nesting problems.

* Makefile.in (AS_FOR_TARGET, LD_FOR_TARGET,
DLLTOOL_FOR_TARGET, WINDRES_FOR_TARGET, AR_FOR_TARGET,
RANLIB_FOR_TARGET, NM_FOR_TARGET): Don't use double quotes to
avoid quotes nesting problems.
(NATIVE_CHECK_MODULES): Ditto, just for consistency.
(DO_X): Export only variables that are set.

From-SVN: r45720