[clang] [clang-format] Add .clang-format.ignore for ignoring files (PR #76327)

[Owen Pan via cfe-commits]

================
@@ -0,0 +1,31 @@
+// RUN: rm -rf %t.dir
+// RUN: mkdir -p %t.dir/level1/level2
+
+// RUN: cd %t.dir
+// RUN: printf "%%s\n" "\*" "level*/*.c*" "*/*2/foo.*" > .clang-format-ignore
----------------
owenca wrote:

```suggestion
// RUN: echo "*" > .clang-format-ignore
// RUN: echo "level*/*.c*" >> .clang-format-ignore
// RUN: echo "*/*2/foo.*" >> .clang-format-ignore
```

https://github.com/llvm/llvm-project/pull/76327