[fix][clang-tidy] fix for r345961 that introduced a test failure on Windows builds

[TWeaver]

Summary

r345961 introduced a path check in .\tools\clang\tools\extra\test\clang-tidy\clang-tidy-run-with-database.cpp.

r345961 added a check line for a path that only handled / on unix machines and not \ on windows machines.

This patch handles both cases.

[TWeaver]

The test failed on the following build bot:

http://lab.llvm.org:8011/builders/llvm-clang-lld-x86_64-scei-ps4-windows10pro-fast/builds/21169

[sammccall]

Thank you!

{{.*}}not-exist also seems fine, up to you.

[TWeaver]

I'm happy as is.

thanks for the review.

[TWeaver]

Oh, I don't have commit access, are you able to commit for me Sam?

Thanks

[JonasToth]

Thank you very much for the patch!
Committed in r345995.

llvm/tools/clang/tools/extra/test/clang-tidy/clang-tidy-run-with-database.cpp

 
 // Regression test: shouldn't crash.
 // RUN: not clang-tidy --checks=-*,modernize-use-nullptr -p %T %T/compilation-database-test/b/not-exist -header-filter=.* 2>&1 | FileCheck %s -check-prefix=CHECK-NOT-EXIST
-// CHECK-NOT-EXIST: Error while processing {{.*}}/not-exist.
+// CHECK-NOT-EXIST: Error while processing {{.*[/\\]}}not-exist.
 // CHECK-NOT-EXIST: unable to handle compilation
 // CHECK-NOT-EXIST: Found compiler error