Fix for PR c++/43375

gcc/cp/ChangeLog:
	PR c++/43375
	* method.c (make_alias_for): Avoid crashing when DECL_LANG_SPECIFIC
	is NULL.
	* decl2.c (vague_linkage_p): Likewise.

gcc/testsuite/g++.dg/ChangeLog:
	PR c++/43375
	* g++.dg/abi/mangle42.C: New test.

From-SVN: r157590