scripts/sphinx-pre-install: cleanup Gentoo checks

On Gentoo, the portage changes for ImageMagick to work are
always suggested, even if already applied. While the two
extra commands should be harmless, add a check to avoid
reporting it without need.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

scripts/sphinx-pre-install

@@ -533,8 +533,19 @@ sub give_gentoo_hints()
 	return if (!$need && !$optional);
 
 	printf("You should run:\n\n");
-	printf("\tsudo su -c 'echo \"media-gfx/imagemagick svg png\" > /etc/portage/package.use/imagemagick'\n");
+
-	printf("\tsudo su -c 'echo \"media-gfx/graphviz cairo pdf\" > /etc/portage/package.use/graphviz'\n");
+	my $imagemagick = "media-gfx/imagemagick svg png";
+	my $cairo = "media-gfx/graphviz cairo pdf";
+	my $portage_imagemagick = "/etc/portage/package.use/imagemagick";
+	my $portage_cairo = "/etc/portage/package.use/graphviz";
+
+	if (qx(cat $portage_imagemagick) ne "$imagemagick\n") {
+		printf("\tsudo su -c 'echo \"$imagemagick\" > $portage_imagemagick'\n")
+	}
+	if (qx(cat $portage_cairo) ne  "$cairo\n") {
+		printf("\tsudo su -c 'echo \"$cairo\" > $portage_cairo'\n");
+	}
+
 	printf("\tsudo emerge --ask $install\n");
 
 }