[NDK] ldrfuncs.h: Add RtlDllShutdownInProgress; make the header C++-compatible (#6071)

The function is added here, because it is loader-related
and thus making sense there, instead of in rtlfuncs.h.

sdk/include/ndk/ldrfuncs.h

@@ -28,6 +28,10 @@ Author:
 #include <ntimage.h>
 #endif
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 //
 // Resource Functions
 //
@@ -59,7 +63,6 @@ LdrEnumResources(
     _Out_writes_to_(*ResourceCount,*ResourceCount) LDR_ENUM_RESOURCE_INFO *Resources
 );
 
-
 NTSTATUS
 NTAPI
 LdrFindResourceDirectory_U(
@@ -144,4 +147,17 @@ LdrEnumerateLoadedModules(
     _In_opt_ PVOID Context
 );
 
+#ifdef NTOS_MODE_USER
+NTSYSAPI
+BOOLEAN
+NTAPI
+RtlDllShutdownInProgress(
+    VOID
+);
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+
 #endif