Bug 1769769 - Don't generate nsIPrintDialogService.h in the source dir. r=jwatt

It seems the order of XPIDL_SOURCES vs. XPIDL_MODULE is important.

Differential Revision: https://phabricator.services.mozilla.com/D146579

widget/moz.build

@@ -89,6 +89,12 @@ elif toolkit == "windows":
         "nsIWinTaskbar.idl",
     ]
 
+if CONFIG["NS_PRINTING"]:
+    # Needs to go before the XPIDL_MODULE line.
+    XPIDL_SOURCES += [
+        "nsIPrintDialogService.idl",
+    ]
+
 TEST_DIRS += ["tests", "tests/gtest"]
 
 DIRS += ["headless"]
@@ -257,9 +263,6 @@ if CONFIG["OS_ARCH"] == "Linux":
     SOURCES += ["LSBUtils.cpp"]
 
 if CONFIG["NS_PRINTING"]:
-    XPIDL_SOURCES += [
-        "nsIPrintDialogService.idl",
-    ]
     EXPORTS += [
         "nsDeviceContextSpecProxy.h",
         "nsPrintSettingsService.h",