Move the point in the code where we handle -fvisibility=hidden. With

the current implementation this should be a nop as explicit visibility
takes precedence in mergeVisibility.

The location chosen is such that attributes checked above it can force
a symbol to be default. For example, an attribute is the variable or function.
Attributes checked after this point, can only make the visibility more
restrictive. An attribute in a type for example.

llvm-svn: 155098