Use libdl.so.2 instead of libdl

Nearly all (or all if only counting LSB conforming) Linux distros have libdl.so.2, and usually don't have a libdl.so symlink unless dev packages are installed.

Fixes dotnet#1492

Author: CasualPokePlayer

src/Core/Silk.NET.Core/Loader/Libdl.cs

@@ -8,7 +8,7 @@ namespace Silk.NET.Core.Loader
 {
     internal static class Libdl
     {
-        private const string LibName = "libdl";
+        private const string LibName = "libdl.so.2";
 
         public const int RtldNow = 0x002;