Adjust log line splitting for shared compiler (#46594)

src/Compilers/Core/MSBuildTask/Csc.cs

@@ -169,7 +169,8 @@ public int WarningLevel
 
         #region Tool Members
 
-        private static readonly string[] s_separators = { Environment.NewLine };
+        // Same separators as those used by Process.OutputDataReceived to maintain consistency between csc and VBCSCompiler
+        private static readonly string[] s_separators = { "\r\n", "\r", "\n" };
 
         internal override void LogMessages(string output, MessageImportance messageImportance)
         {