Add hasExternalLinkageUncached back with the test that Richard provided, but
keep the call at the current location.

llvm-svn: 178741
diff --git a/clang/test/Modules/Inputs/linkage-merge-foo.h b/clang/test/Modules/Inputs/linkage-merge-foo.h
new file mode 100644
index 0000000..7ed7775
--- /dev/null
+++ b/clang/test/Modules/Inputs/linkage-merge-foo.h
@@ -0,0 +1 @@
+int f();