gccrs: Make globbing definition shadowable by default
Elements from glob use declaration shall be shadowable by default.
gcc/rust/ChangeLog:
* resolve/rust-forever-stack.h: Add a new function prototype to insert
a shadowable definition.
* resolve/rust-forever-stack.hxx: Add the new insert_shadowable
function to insert shadowable definition into the forever stack.
* resolve/rust-name-resolution-context.cc (NameResolutionContext::insert_shadowable):
Likewise with the name resolution context.
* resolve/rust-name-resolution-context.h: Add name resolution context
insert_shadowable member function prototype.
* resolve/rust-toplevel-name-resolver-2.0.cc (GlobbingVisitor::visit):
Insert shadowable definition into the forever stack for glob use
declaration.
Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>