PR c++/47877 - -fvisibility-inlines-hidden and member templates.
DECL_VISIBILITY_SPECIFIED is also true if an enclosing scope has explicit
visibility, and we don't want that to override -fvisibility-inlines-hidden.
So check for the attribute specifically on the function, like we already do
for template argument visibility restriction.
* decl2.c (determine_visibility): -fvisibility-inlines-hidden beats
explicit class visibility for a template.