c++: inline variables and modules

We weren't writing out the definition of an inline variable, so the importer
either got an undefined symbol or 0.

gcc/cp/ChangeLog:

	* module.cc (has_definition): Also true for inline vars.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/inline-1_a.C: New test.
	* g++.dg/modules/inline-1_b.C: New test.