[modules] Even if we already have a definition of a class, loading in another
one can give us more lookup results (due to implicit special members). Be sure
to complete the redecl chain for every kind of DeclContext before performing a
lookup into it, rather than only doing so for NamespaceDecls.

llvm-svn: 230558
diff --git a/clang/test/Modules/Inputs/merge-decl-context/merge-decl-context.modulemap b/clang/test/Modules/Inputs/merge-decl-context/merge-decl-context.modulemap
new file mode 100644
index 0000000..fedc5df
--- /dev/null
+++ b/clang/test/Modules/Inputs/merge-decl-context/merge-decl-context.modulemap
@@ -0,0 +1,13 @@
+module "a" {
+  textual header "a.h"
+}
+
+module "b" {
+  export *
+  header "b.h"
+}
+
+module "c" {
+  export *
+  header "c.h"
+}