testing/horizon: fix ftbfs

Due to `-Werror`, this fails to build on gcc >= 10.0.1. This has been
[reported][0] to json upstream, and fixed in this [pr][1].

Backport the fix to horizon

[0]:nlohmann/json#1939
[1]:nlohmann/json#2144

testing/horizon/APKBUILD

@@ -18,7 +18,9 @@ makedepends="bcnm-dev boost-dev cmake curl-dev eudev-dev libarchive-dev
 	linux-headers parted-dev skalibs-dev util-linux-dev libxkbfile-dev"
 subpackages="$pkgname-image $pkgname-dbg $pkgname-dev $pkgname-doc
 	$pkgname-tools"
-source="https://code.foxkit.us/adelie/horizon/-/archive/$pkgver/horizon-$pkgver.tar.gz"
+source="https://code.foxkit.us/adelie/horizon/-/archive/$pkgver/horizon-$pkgver.tar.gz
+	json-cast-character-to-unsigned-for-comparrison.patch
+	"
 
 build() {
 	if [ "$CBUILD" != "$CHOST" ]; then
@@ -124,4 +126,5 @@ PROFILE
 		"$subpkgdir"/usr/share/xsessions/horizon.desktop
 }
 
-sha512sums="3ff46980387454f85a326ac3ea123b55cf16fc339faec48fdc77f10334e0bd93e8cf51e6adeed516d2e4309cf4426b9d1ac6760cdd479b196a5f4aa33c1f3a28  horizon-0.9.6.tar.gz"
+sha512sums="3ff46980387454f85a326ac3ea123b55cf16fc339faec48fdc77f10334e0bd93e8cf51e6adeed516d2e4309cf4426b9d1ac6760cdd479b196a5f4aa33c1f3a28  horizon-0.9.6.tar.gz
+5ab7a35d239210e031739c4149fd8e68570ea0efd278a2eac9330d6e30c601d1310b9c17523563a41424c2a8aa2452e5a9bcbce5d8087330d2697cd1b77b312f  json-cast-character-to-unsigned-for-comparrison.patch"

testing/horizon/json-cast-character-to-unsigned-for-comparrison.patch

@@ -0,0 +1,19 @@
+Description: GCC 10.0.1 started to warn on redundant comparisons. Horizon
+builds with -Werror, so this warning is turned into an error. Upstream fixed this,
+so backport to Horizon.
+
+Based on https://github.com/nlohmann/json/pull/2144/commits/23051df2c71dd3f9698e01de3cbfab0034c6e50e
+
+diff --git a/3rdparty/json.hpp b/3rdparty/json.hpp
+index 06da815..58e3f27 100644
+--- a/3rdparty/json.hpp
++++ b/3rdparty/json.hpp
+@@ -8491,7 +8491,7 @@ scan_number_done:
+         std::string result;
+         for (const auto c : token_string)
+         {
+-            if ('\x00' <= c and c <= '\x1F')
++            if (static_cast<unsigned char>(c) <= '\x1F')
+             {
+                 // escape control characters
+                 std::array<char, 9> cs{{}};