Allow system ssl to be used for ngtcp2

Move `libressl` into a feature like `curl`.

Author: donny-dont

WindowsRequirements.json

@@ -3,7 +3,7 @@
     "brotli",
     "libressl[tools]",
     "nghttp2",
-    "ngtcp2",
+    "ngtcp2[libressl]",
     "nghttp3",
     "curl[libressl,http3,ipv6]",
     "icu",

ports/ngtcp2/portfile.cmake

@@ -24,6 +24,13 @@ else ()
     set(NGTCP2_STATIC_LIB OFF)
 endif ()
 
+# Each port of an OpenSSL equivalent checks to see that no other variant is installed so
+# just check to see if any OpenSSL variants are requested and if not use the system one
+set(USE_OPENSSL ON)
+if (NOT libressl IN_LIST FEATURES)
+    message(STATUS "Using system SSL library")
+endif ()
+
 vcpkg_configure_cmake(
     SOURCE_PATH ${SOURCE_PATH}
     PREFER_NINJA

ports/ngtcp2/vcpkg.json

@@ -5,7 +5,6 @@
   "homepage": "https://github.com/ngtcp2/ngtcp2",
   "license": "MIT",
   "dependencies": [
-    "libressl",
     {
       "name": "vcpkg-cmake",
       "host": true
@@ -18,5 +17,13 @@
       "name": "vcpkg-cmake-webkit",
       "host": true
     }
-  ]
+  ],
+  "features": {
+    "libressl": {
+      "description": "SSL support through libressl. If no SSL libraries are specified then the system SSL library will be used.",
+      "dependencies": [
+        "libressl"
+      ]
+    }
+  }
 }