Debug Info: Add a file: field to DIImportedEntity.

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.

<rdar://problem/33357889>
https://bugs.llvm.org/show_bug.cgi?id=33822

Differential Revision: https://reviews.llvm.org/D35583

llvm-svn: 308398
diff --git a/llvm/test/DebugInfo/X86/lexical-block-file-inline.ll b/llvm/test/DebugInfo/X86/lexical-block-file-inline.ll
index 0f85a55..9f040f4 100644
--- a/llvm/test/DebugInfo/X86/lexical-block-file-inline.ll
+++ b/llvm/test/DebugInfo/X86/lexical-block-file-inline.ll
@@ -134,7 +134,7 @@
 !8 = distinct !DISubprogram(name: "foo", linkageName: "_Z3foov", scope: !9, file: !9, line: 6, type: !5, isLocal: false, isDefinition: true, scopeLine: 6, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
 !9 = !DIFile(filename: "test.h", directory: "/")
 !10 = !{!11}
-!11 = !DIImportedEntity(tag: DW_TAG_imported_module, scope: !12, entity: !14, line: 1)
+!11 = !DIImportedEntity(tag: DW_TAG_imported_module, scope: !12, entity: !14, file: !1, line: 1)
 !12 = !DILexicalBlockFile(scope: !13, file: !9, discriminator: 0)
 !13 = distinct !DILexicalBlock(scope: !4, file: !1, line: 3)
 !14 = !DINamespace(name: "N", scope: null)