[modules] Tests for r245390.

llvm-svn: 245391
diff --git a/clang/test/Modules/Inputs/explicit-build-overlap/def.map b/clang/test/Modules/Inputs/explicit-build-overlap/def.map
new file mode 100644
index 0000000..444faf7
--- /dev/null
+++ b/clang/test/Modules/Inputs/explicit-build-overlap/def.map
@@ -0,0 +1,2 @@
+module a { textual header "a.h" }
+module b { header "a.h" header "b.h" }