build: Fix some paths in uninstall-libs

Folder and file names weren't being separated with a slash.
This resulted in .dll.a, .lib and .def files not being removed on uninstall.

Signed-off-by: Alexander Strasser <eclipse7@gmx.net>
(cherry picked from commit 49440853d0)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

library.mak

@@ -84,8 +84,8 @@ uninstall-libs::
 	-$(RM) "$(SHLIBDIR)/$(SLIBNAME_WITH_MAJOR)" \
 	       "$(SHLIBDIR)/$(SLIBNAME)"            \
 	       "$(SHLIBDIR)/$(SLIBNAME_WITH_VERSION)"
-	-$(RM) $(SLIB_INSTALL_EXTRA_SHLIB:%="$(SHLIBDIR)"%)
-	-$(RM) $(SLIB_INSTALL_EXTRA_LIB:%="$(LIBDIR)"%)
+	-$(RM)  $(SLIB_INSTALL_EXTRA_SHLIB:%="$(SHLIBDIR)/%")
+	-$(RM)  $(SLIB_INSTALL_EXTRA_LIB:%="$(LIBDIR)/%")
 	-$(RM) "$(LIBDIR)/$(LIBNAME)"
 
 uninstall-headers::