Add stub modulemaps for windows.

include/cling/libc.modulemap

@@ -1,4 +1,6 @@
 module "libc" [system] [extern_c] [no_undeclared_includes] {
+  requires !msvc
+
   export *
   module "assert.h" {
     export *

include/cling/libc_msvc.modulemap

@@ -0,0 +1,14 @@
+module "libc" [system] [extern_c] [no_undeclared_includes] {
+  requires msvc
+
+  export *
+  module "assert.h" {
+    export *
+    textual header "assert.h"
+  }
+  module "string.h" {
+    export *
+    header "string.h"
+  }
+  // FIXME: Add the rest of the headers
+}

include/cling/std.modulemap

@@ -1,4 +1,6 @@
 module "std" [system] {
+  requires !msvc
+
   export *
   module "algorithm" {
     export *

include/cling/std_msvc.modulemap

@@ -0,0 +1,14 @@
+module "std" [system] {
+  requires msvc
+
+  export *
+  module "algorithm" {
+    export *
+    header "algorithm"
+  }
+  module "array" {
+    export *
+    header "array"
+  }
+  // FIXME: Add the rest of the headers
+}

lib/Interpreter/CIFactory.cpp

@@ -632,10 +632,18 @@ namespace {
     }
 
     std::string MOverlay;
+#ifdef LLVM_ON_WIN32
+    maybeAppendOverlayEntry(cIncLoc.str(), "libc_msvc.modulemap",
+                            clingIncLoc.str(), MOverlay);
+    maybeAppendOverlayEntry(stdIncLoc.str(), "std_msvc.modulemap",
+                            clingIncLoc.str(), MOverlay);
+#else
     maybeAppendOverlayEntry(cIncLoc.str(), "libc.modulemap", clingIncLoc.str(),
                             MOverlay);
     maybeAppendOverlayEntry(stdIncLoc.str(), "std.modulemap", clingIncLoc.str(),
                             MOverlay);
+#endif // LLVM_ON_WIN32
+
     if (!tinyxml2IncLoc.empty())
       maybeAppendOverlayEntry(tinyxml2IncLoc.str(), "tinyxml2.modulemap",
                               clingIncLoc.str(), MOverlay);