libstdc++.exp (v3-build_support): Use env(AR) and env(RANLIB), not env(AR_FOR_TARGET) and env(RANLIB_FOR_TARGET).

	* testsuite/lib/libstdc++.exp (v3-build_support): Use env(AR)
	and env(RANLIB), not env(AR_FOR_TARGET) and env(RANLIB_FOR_TARGET).

From-SVN: r126392