scripts: sphinx-pre-install: address some issues with Gentoo

There are some small misdetections with Gentoo. While they
don't cause too much trouble, it keeps recomending to
install things that are already there.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/7f631edce102b02ccbdbfb18be1376a86b41373d.1586883286.git.mchehab+huawei@kernel.orgSigned-off-by: Jonathan Corbet <corbet@lwn.net>

scripts/sphinx-pre-install

@@ -560,7 +560,8 @@ sub give_gentoo_hints()
 			   "media-fonts/dejavu", 2) if ($pdf);
 
 	if ($pdf) {
-		check_missing_file(["/usr/share/fonts/noto-cjk/NotoSansCJKsc-Regular.otf"],
+		check_missing_file(["/usr/share/fonts/noto-cjk/NotoSansCJKsc-Regular.otf",
+				    "/usr/share/fonts/noto-cjk/NotoSerifCJK-Regular.ttc"],
 				   "media-fonts/noto-cjk", 2);
 	}
 
@@ -575,10 +576,10 @@ sub give_gentoo_hints()
 	my $portage_imagemagick = "/etc/portage/package.use/imagemagick";
 	my $portage_cairo = "/etc/portage/package.use/graphviz";
 
-	if (qx(cat $portage_imagemagick) ne "$imagemagick\n") {
+	if (qx(grep imagemagick $portage_imagemagick 2>/dev/null) eq "") {
 		printf("\tsudo su -c 'echo \"$imagemagick\" > $portage_imagemagick'\n")
 	}
-	if (qx(cat $portage_cairo) ne  "$cairo\n") {
+	if (qx(grep graphviz $portage_cairo 2>/dev/null) eq  "") {
 		printf("\tsudo su -c 'echo \"$cairo\" > $portage_cairo'\n");
 	}