DIImportedEntity has a line number, but not a file field. To determine the decl_line/decl_file we combine the line number from the DIImportedEntity with the file from the DIImportedEntity's scope. This does not work correctly when the parent scope is a DINamespace or a DIModule, both of which do not have a source file.
This patch adds a file field to DIImportedEntity to unambiguously identify the source location of the using/import declaration.
Most testcase updates are mechanical, the interesting one is the removal of the FIXME in test/DebugInfo/Generic/namespace.ll.
This fixes PR33822. See https://bugs.llvm.org/show_bug.cgi?id=33822 for more context.