Pass lib path from run script as env. var and read it in DLIR

It's always set by the run script, but I've added a fallback in case someone
hardcodes the mono command in a .desktop or something

Assets/EmuHawkMono.sh

@@ -20,6 +20,7 @@ if [ -z "$libpath" ]; then
 fi
 if [ -z "$winepath" ]; then winepath="$libpath/wine"; fi
 export LD_LIBRARY_PATH="$PWD/dll:$PWD:$winepath:$libpath"
+export BIZHAWK_INT_SYSLIB_PATH="$libpath"
 if [ "$1" = "--mono-no-redirect" ]; then
 	shift
 	printf "(received --mono-no-redirect, stdout was not captured)\n" >EmuHawkMono_laststdout.txt

src/BizHawk.Common/IImportResolver.cs

@@ -24,10 +24,11 @@ namespace BizHawk.Common
 		static DynamicLibraryImportResolver()
 		{
 			var currDir = Path.GetDirectoryName(Assembly.GetExecutingAssembly().CodeBase)?.Replace("file:", "") ?? string.Empty;
+			var sysLibDir = Environment.GetEnvironmentVariable("BIZHAWK_INT_SYSLIB_PATH") ?? "/usr/lib";
 			UnixSearchPaths = new[]
 			{
 				$"{currDir}/", $"{currDir}/dll/",
-				"/usr/lib/bizhawk/", "/usr/lib/", "/usr/lib/mupen64plus/"
+				$"{sysLibDir}/bizhawk/", $"{sysLibDir}/", $"{sysLibDir}/mupen64plus/"
 			};
 		}