[Wayland] Fall back to ftruncate if posix_fallocate isn't supported by filesystem.

diff --git widget/gtk/WindowSurfaceWayland.cpp widget/gtk/WindowSurfaceWayland.cpp
index 9a73326399bd5..9e42a7f1c5d18 100644
--- widget/gtk/WindowSurfaceWayland.cpp
+++ widget/gtk/WindowSurfaceWayland.cpp
@@ -221,7 +221,9 @@ static int WaylandAllocateShmMemory(int aSize) {
   do {
     ret = posix_fallocate(fd, 0, aSize);
   } while (ret == EINTR);
-  if (ret != 0) {
+  if (ret == 0) {
+    return fd;
+  } else if (ret != ENODEV && ret != EINVAL && ret != EOPNOTSUPP) {
     NS_WARNING(
         nsPrintfCString("posix_fallocate() fails to allocate shm memory: %s",
                         strerror(ret))
@@ -229,7 +231,7 @@ static int WaylandAllocateShmMemory(int aSize) {
     close(fd);
     return -1;
   }
-#else
+#endif
   do {
     ret = ftruncate(fd, aSize);
   } while (ret < 0 && errno == EINTR);
@@ -240,7 +242,6 @@ static int WaylandAllocateShmMemory(int aSize) {
     close(fd);
     fd = -1;
   }
-#endif
 
   return fd;
 }
@@ -253,7 +254,7 @@ static bool WaylandReAllocateShmMemory(int aFd, int aSize) {
   do {
     errno = posix_fallocate(aFd, 0, aSize);
   } while (errno == EINTR);
-  if (errno != 0) {
+  if (errno != 0 && errno != ENODEV && errno != EINVAL && errno != EOPNOTSUPP) {
     return false;
   }
 #endif