rtl: fixed building for namespaced win64

rtl/win64/Makefile

@@ -3054,3 +3054,6 @@ BUILDRTL_DEPS=buildrtl.pp $(SYSTEMUNIT)$(PPUEXT) $(OBJPASUNIT)$(PPUEXT) $(WINDOW
 	      $(BUILDRTL_DEPS_OS) $(BUILDRTL_DEPS_CPU)
 buildrtl$(PPUEXT) : $(BUILDRTL_DEPS)
 	$(COMPILER) $(BUILDUNITPATHS) $(BUILDINCLUDEPATHS) $(BUILDRTL_OPT) $<
+WinApi.Signals$(PPUEXT) : $(NSWINDOWSDIR)/WinApi.Signals.pp
+	$(COMPILER) $<
+

rtl/win64/Makefile.fpc

@@ -126,4 +126,6 @@ BUILDRTL_DEPS=buildrtl.pp $(SYSTEMUNIT)$(PPUEXT) $(OBJPASUNIT)$(PPUEXT) $(WINDOW
 buildrtl$(PPUEXT) : $(BUILDRTL_DEPS)
 	$(COMPILER) $(BUILDUNITPATHS) $(BUILDINCLUDEPATHS) $(BUILDRTL_OPT) $<
 
+WinApi.Signals$(PPUEXT) : $(NSWINDOWSDIR)/WinApi.Signals.pp
+	$(COMPILER) $<