[mlir:PDLL] Use normalized paths in compilation database test

This fixes issues with the compilation database when the file path
isn't in the correct form.

mlir/test/mlir-pdll-lsp-server/compilation_database.test

@@ -1,4 +1,4 @@
-// RUN: echo -e '--- !FileInfo:\n  filepath: "/foo.pdll"\n  includes: "%S;%S/../../include"' > %t.yml
+// RUN: echo -e '--- !FileInfo:\n  filepath: "/foo.pdll"\n  includes: "%/S;%/S/../../include"' > %t.yml
 // RUN: mlir-pdll-lsp-server -pdll-compilation-database=%t.yml -lit-test < %s | FileCheck %s
 {"jsonrpc":"2.0","id":0,"method":"initialize","params":{"processId":123,"rootPath":"pdll","capabilities":{},"trace":"off"}}
 // -----