[modules] If we're treating an elaborated-type-specifier as if it introduces a

[modules] If we're treating an elaborated-type-specifier as if it introduces a
tag (because the previous declaration was found in a different module), inject
the tag into the appropriate scope (that is, the enclosing scope if we're in a
function prototype scope in C++).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@257251 91177308-0d34-0410-b5e6-96231b3b80d8