[clang] [clang-format] Make ignored files unformatted instead of empty. (PR #170416)

[via cfe-commits]

================
@@ -46,15 +46,19 @@
 // CHECK5-NEXT: {{Formatting \[4/5] .*foo\.c}}
 // CHECK5-NOT: foo.js
 
+// Check that ignored files are unformatted, but still output.
 // RUN: echo "foo.*" > .clang-format-ignore
 // RUN: echo "int i ;" > foo.c
 // RUN: clang-format -assume-filename=foo.c < foo.c \
----------------
owenca wrote:

```suggestion
// RUN: clang-format -assume-filename=foo.c < foo.c | diff foo.c -
```

https://github.com/llvm/llvm-project/pull/170416