Declare some MSI functions.

diff --git a/include/msi.h b/include/msi.h
index b33f2b4..b2e36e1 100644
--- a/include/msi.h
+++ b/include/msi.h
@@ -98,4 +98,8 @@
 UINT WINAPI MsiVerifyPackageW(LPCWSTR);
 #define     MsiVerifyPackage WINELIB_NAME_AW(MsiVerifyPackage)
 
+INSTALLSTATE WINAPI MsiQueryProductStateA(LPCSTR);
+INSTALLSTATE WINAPI MsiQueryProductStateW(LPCWSTR);
+#define     MsiQueryProductState WINELIB_NAME_AW(MsiQueryProductState)
+
 #endif /* __WINE_MSI_H */