Bug 1745384 - Temporarily fix crash during clang mingw cross compile builds. r=gfx-reviewers,lsalzman

It appears that dom/canvas/nsICanvasRenderingContextInternal.cpp must be
part of a greater unified build file. Adding new files has pushed it
into its own unified file causing clang to crash when cross compiling
using mingw. For now, let's just put the new file a previous patch added
into SOURCES instead of UNIFIED_SOURCES to avoid breaking this delicate
balance.

A follow up bug will need to be created to investigate on the clang
side.

Differential Revision: https://phabricator.services.mozilla.com/D133487

dom/canvas/moz.build

@@ -89,13 +89,13 @@ UNIFIED_SOURCES += [
     "ImageData.cpp",
     "nsICanvasRenderingContextInternal.cpp",
     "OffscreenCanvas.cpp",
-    "OffscreenCanvasDisplayHelper.cpp",
     "XRWebGLLayer.cpp",
 ]
 
 SOURCES += [
     "DrawTargetWebgl.cpp",  # Isolate Skia
     "ImageUtils.cpp",
+    "OffscreenCanvasDisplayHelper.cpp", # Clang mingw cross compile crash, see bug 1745384
 ]
 
 # WebGL Sources