PR c/89933
c/
	* c-decl.c (merge_decls): When newdecl's type is its main variant,
	don't try to remove it from the variant list, but instead assert
	it has no variants.
cp/
	* decl.c (duplicate_decls): When newdecl's type is its main variant,
	don't try to remove it from the variant list, but instead assert
	it has no variants.
testsuite/
	* c-c++-common/pr89933.c: New test.

From-SVN: r270329