Arch Linux

Description:

Arch clang does not color diagnostics, while the upstream clang does when using flags `-Xclang -fcolor-diagnostics -c` and redirecting stderr through a pipe. The expected behavior of clang is to color the diagnostics regardless of the fact that stderr is not some tty.

However, if I remove `-Xclang` or `-c` it works i.e. both `clang++ -fcolor-diagnostics -c foo.cc 2>&1 | cat` and `clang++ -Xclang -fcolor-diagnostics foo.cc 2>&1 | cat` give colored output.

I cannot reproduce this behavior using the official clang build: https://github.com/llvm/llvm-project/releases/download/llvmorg-11.0.1/clang+llvm-11.0.1-x86_64-linux-gnu-ubuntu-20.10.tar.xz

Additional info:
* package version: 11.0.1-1

Steps to reproduce:

1. Create file `foo.cc` with below content:
```
int main() {
return "";
}
```
2. Run: `clang++ -Xclang -fcolor-diagnostics -c foo.cc 2>&1 | cat`